Best temperature for optimum tube performance

Is there an optimum temperature range in which tubes perform best?
I've been running tube amps/preamps for over 40 years and have always placed a small, quiet fan in front of them to prevent excessive heat build-up (a modified, two-door antique silver cabinet is where they reside).
I'm aware that electrical resistance increases in proportion to increasing temperature, but am I somehow decreasing the optimum performance of my tube components with this strategy?
So what you do, get one of those temperature guns and listen. Play a record, record the temp, play the record, record the temp. Repeat until either you hear a difference or you don't. Report back here- where fifty people who have never bothered to compare anything their whole life will rip you apart for your expectation bias and sloppy experimental technique.   

Either that or just run the fan and call it good.
No idea really but tube amps are shedding considerable heat. I think that  in the vacuum atmosphere of a vacuum tube normal room temperatures don't affect the tubes operation all that much if any. Your fan set-up will cool the chassis and components but one can't guess how uniform or effective that will be. I make sure all my tube equipment is not enclosed in any cabinet, just too much heat for electronic components.  
Best is putting tube amps on the dedicated stand for better tube life and air flow.
Report back here- where fifty people who have never bothered to compare anything their whole life will rip you apart for your expectation bias and sloppy experimental technique.
MC, why can't you just make a suggestion without adding in a comment of how stupid or ignorant or insensate other people are? You have experience and knowledge and you are willing share it. Why must you snark? Something not going right for you? 
A new band, Snarky MC?

Just kidding loved the use of “snark”

I enjoy MC posts and his view.
Why fan at the front and at the back where more heat would be injected out from the cabinet?
Output tubes and even signal ones produce considerable amount of heat stressing close by components like caps. If you cannot move equipment in open air then what you did is fine but it is difficult to tell if the cooling is uniform.
All tube spec sheets provide data at a specified ambient temperature. So if within that temperature they should work as intended.

Check it out: people taking this seriously. People who most of them never even notice a difference as their components warm up. People who will argue and deny there even IS any difference as a component warms up. But here they are imagining all kinds of crazy theories about how to optimize this imaginary tube temperature performance envelope.   

Sentence first, verdict afterward! Lewis Carroll knows you guys all too well. 

A snark, a snark! My Kingdom for a snark!
The tubes don’t mind the heat too much. The passive components like electrolytic capacitors would prefer it a little cooler. Although if you’ve been doing it for 40 years in that cabinet, with a fan, you’re probably fine. Just don't tell them that if you ever make a warranty claim.
It takes very little air flow to cool a chassis significantly. I've been doing it since the 70's. A couple of 12v 60mm PC cooler fans running on 3.5v are completely silent and cool the internal chassis from 50°C to 30°C on my tweeter PrimaLuna PL-5. Ditto a 100mm on midrange VTA M-125s.
M-125: - note fan under tubes at front.
Thank you one and all for weighing in...
As an aside, I drilled a series of 1-1/4” holes in the upper back of the cabinet to provide convection venting....the two independent top drawers hide those holes.
I did install a small, quiet computer fan but it just couldn’t pull enough air to keep the gear from cooking.
(I was petrified to see millercarbon had replied.... I remain yet to witness the dust-ups he provokes.)
The temp gun is a great idea....
I use one of their component fans with front exhaust on my Parasound 5 channel SS amp. They have other fans for cabinets.
Wow, those fan solutions are very inexpensive. Imagine if they were sold by Synergistic et al?
I can only add this... I have an Audio Research D160 tube amp from the early eighties, 1982 to be exact. It uses 6550 tubes biased to 65 mV, according to factory specs. Way to hot for any practical life. I have "detuned" them to 46-48 mV to calm things down while maintaining proper gain.  The amp came equipped with two fans to bathe the tubes in cool air.  And naturally, per the owner's manual, the amp takes a couple hours of use to achieve thermal equalibrium. Use this to your benefit. The detuning and the fans really help in this specific example.

Happy listening
Fall, Winter, Spring, CHANGE! That's me. I can't take the heat, and I can't take the noise from the fans or AC in the Summer.. I change amp types, plane and simple. Class D are just fine with a little tweak here and there for the 3-4 months of heat.. 

I look over the valve amps, make any changes I want to do.. Then they go back in service around Halloween. If we have a party here, after the party.. :-)

Sometimes I sneak out my MC240 or 225 in the summer, play the Beach Boys, on the deck. Pair of old Heresy's or something. It just works.  

Ever look at a "combo" guitar amp? For example, a Fender Twin Reverb (I’ve owned and abused a couple of these) has 4 6L6 power tubes and 6 preamp tubes, all mounted upside down venting heat into the amp (although they’re uncovered...still...), and if you tilt it back it’s worse heat wise...but my amps never failed to work tirelessly. Kinda makes hifi stuff look weirdly delicate and wimpy...vibration? The amp is also in the same space as 2 12" speakers and still manages to work...all night...
My three ARC amps (NOT TUBES) each have 32 output transistors and 3 cooling fans each.  So, 96 output transistors and nine cooling fans.  If I run them really hard for say an hour their temp never goes over 100 F.  Yes, I measure them with a BBQ probe remotely.

Although this does not speak to tubes directly, I would say that if the interior of your cabinet is close to the ambient temperature of the room
you are good to go.

A remote thermometer is very cheap and worth it if you are asking the question.  Start out cold and log the temps against time as well as noting room temp.

Let the snarking begin!

Put your gear in a ventilated wood rack and watch how much better your tube gear sounds.
Okay so look, all these replies and only ONE (mine!) actually addresses the OPs question: Is there an optimum temperature range in which tubes perform best?

No one else attempted so much as to even consider this question! Only me! And with the only answer that really makes any sense: check temps, listen, and see! Even explained how to do it!  

Only thing I got wrong, too optimistic. Assumed this being an audiophile site and the OP pretending to care, he (or someone, anyone!) might actually try and see. Right! That'll be the day! However, because I thought just maybe someone might actually BE an AUDIOPHILE they would maybe try.... and then the flying monkeys would rip him apart for having the temerity to say what he heard. For not being double-blind enough. For expecting something might or might not happen. For whatever. On and on. All the usual stories guys blather to avoid having to actually, you know, LEARN SOMETHING!  

For not lowering my standards enough, I do apologize. Will try to do better, by which I mean worse, going forward.  
The simple answer is no. 
Always provide gear adequate ventilation.   Especially tube gear and power amps.  They generate the most heat. 
For not lowering my standards enough, I do apologize. Will try to do better, by which I mean worse, going forward.  
Not possible
The filament of the tube is intimately associated with the cathode of the tube which it heats. Room temperature isn’t going to affect them much at all so I wouldn’t worry about that. But a fan is a good idea because heat does wear tubes out, and it also shortens the life of electrolytic capacitors (which are used in the power supply).

Now there is an optimal filament voltage- because that is what controls the cathode temperature. But the lifespan of the tube should be considered also. If the filament voltage is slightly lower you’ll get longer life, just like a light bulb. But if its too low, you can damage the cathode. There are a lot of variables here and this is really the sort of thing that is up to the designer. But as far as a fan goes, its a good practice regardless of tube or solid state.
One of my better purchases for my system is this exhaust fan that’s built to be placed on top of audio components and is extremely quiet.. It has 3 fans that suck the hot air up and blow it out either the front or back depending on the unit. It has an LED temperature gauge to measure the internal temp of the component and you set it like a thermostat to the temp you want and it then cycles on/off to maintain that temperature.  I use two of them on placed top of my tube amps.  And did I say it’s quiet?  It’s brilliant. 
AC Infinity AIRCOM T10, Quiet Cooling Blower Fan System 17" Front-Exhaust, for Receivers, Amps, DVR, AV Cabinet Components