You voud buy both and compare, but that would be hard...
I agree with a lot of the opinions here. I have AMD Athlon 64 3700+, and I'm cruising at 2.2 GHz at the same speed that an Intel would at appx. 3 GHz. Apparently, according to the techhie at Frys it's because of higher efficiency than the Intels... but I'll have to look up the exact reason...