I have been running 2 Celerons at 551 2.1 volts 68 FSB according to BP6FSB utility. Each processor has a globalwin cooler. 32 degrees with the case off (and who really leaves the case on???) and 43 with it on.
I got bold one day and tried to push to 750 mhz to see what would happen using FSB utility... When it crashed and rebooted the bios looked like it got whacked . I powered down and restarted and it all came back. Needless to say I haven't tried that again!
I am itching to get a couple of 500 ans push that to 700+. All in the name of SETI