The gang at Tech Report have a review up of the 3800+ Athlon 64 Venice core processor. 
Perhaps we saw relatively lackluster results because we used Prime95’s stringent torture test with small FFTs, which will cause a shaky CPU to throw an error even when it will run other programs with no apparent problems. We also used Windows XP x64 Edition for testing, which make uses of transistors that would be dormant in a 32-bit OS, potentially exposing a problem. Or maybe our chip was just a dog. Whatever the cause, 2.7GHz was the practical limit for us.