How far over the limit can I go

I used to have a set of Manley Neoclassic 250s. Turned it on with an old set of tubes one day and BAM! Power tube went down swinging and took out a resistor. Luckily Manley sold these clip on replacements so I was able to get them replaced myself. Always a risk with old tubes. 

IF/When you decide to try and keep tube gear: Buy a simple tube tester!!!!!

Give yourself the easy confidence of knowing simple: short, no short, good, bad, how strong, matched tubes similar strength.

I have a big fancy one gathering dust because my simple portable one and the big one always agree.

https://www.ebay.com/itm/124523483585?hash=item1cfe2d91c1:g:6hYAAOSwKm9f~K3J

some tubes can not be tested on older units, check for that.

btw, what do you mean 2,000. hours. What tubes? Many, many tubes last 10,000. hours

Better safe than sorry. Pay to play.

Have the same set of tubes in my CAT preamp since 2016, about 10,000 hrs. Still going strong. (Mullard 12AX7 reissue, Reflektor 6922). 

The answer is they could fail tomorrow or not.