if you do alot of gaming benchmarks and have good eyes then you could probably see some sort of difference! it would only be like a couple of extra frames per second or something like that! for normal programs, just probably a couple seconds less loading the higher CPU it is! i currently run a AMD 2800 and got it clocked to 3000 speeds and ive only just noticed a teeny tiny improvement in speed!
I would suggest probably only noticeable difference is price. Having said that, I went through the same thought process in August this year and, took the "middle way" and bought a system with an AMD 2800, which flies.