Most folks will try to flame me on this one, but anyway.....
I have pushed my old 80486DX-25 all the way to 40Mhz with OUT a fan or heatsink. It ran for all of its life (2 years), no it didn't die. It kinda makes you
wonder how intel sorts its chips. I guess if they could get away with selling
it at 33mhz they would. It just means more $$$$. I still have the processor
and it is for sale.......
I just upgraded to a 80486DX2-66 and yes, I have jammed it up to 40Mhz with a
heatsink and fan and it runs just fine. It ran without problems for a few hours, although I will have to admit, I'm somewhat paranoid so I lowered it to back down to 33Mhz.
I used to work for a PC clone vendor and we used to try to torture the boards
to death in the design verification department. Of course if the board/processor blew, my home-system would still be running.....