I'm mainly using two computers. Older one has an asus p4p800, newer one is a shuttle xpc, both have [socket 478] type cpu sockets.. When I got the newer machine I moved the p4 2.6ghz cpu from the old p4p800 machine to the xpc. That cpu used to work at 3.2ghz for more than two years but now anything above 2.8ghz causes instabilities with the xpc.
I also placed a new p4 3.0ghz cpu to the 2yr old p4p800 asus board and it's now working flawlessly as a 3.7ghz beast!
edit: but reading the original post I realized these weren't your worries. In any case something you can overclock to the extreme is guaranteed to work perfectly when not overclocked.