I think Prime95 is still one of the best out there for ultimate stability. I run CPUBurn 4 at the same time to maximize heat. I have had it fail in Prime95, when CPUBurn wouldn't crash your system, which is how CPUBurn lets you know its not stable.
3DMARK is also good to test other factors. Your processor might be stable, but your high fsb is causing your video card to error condition. It tests for those kind of errors.
Funny thing, I get alot of I.E. errors when I am running on the edge of stability, so you might add that to the list..............

J/K
Memtest-86 is a good test for your memory.