I'm basically looking for something that is the cpu equivalent of memtest
for memory.

I don't usually have access to a bootable windows partition and besides, I
want to test the cpu independently of windows. I'd ideally like something
that just runs through every instruction and maybe runs a few quick
benchmarks. I'm not interested in stressing the cpu. If it's error free
after 20 minutes, that's good enough for me.

For example, I have a celeron 1100 with a missing pin that POSTs just fine.
But that doesn't me it won't crash the system everytime it tries to execute
a certain instruction, or maybe when it tries to go into standby. I've no
idea what all the pins on a cpu do, I just want to know if the missing pin
will cause a problem.

And this is a general question, as I have lots of cpus pass through my hands
that I need to check just as easily as I can check memory with memtest.

BTW I don't much care about diagnostics telling me if the cpu has mmx etc.
I just want to know if it's 100% at default speeds.