Best temperature for optimum tube performance

Room temperature?? Never concerned myself with this really. 

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.