This is a good thread.

But seriously guys, what does the AMD CPU driver contribute to the "smoothness"?

I noticed today when testing/benching my new X4 940 that every 3D-bench stuttered worse than any Intel rig I've ever owned.

Since I had swapped MB from my () DFI Jr 790GX-M2RS to Asus M3A78-EM I wondered if I needed to reinstall the AMC CPU driver.
Sure enough.
After (re)installing this everything went "buttersmooth". No hick-ups.. just smoooooth framerates.
AFAIK there is no similar "CPU driver" for an Intel CPU(multi-core).

Could this be the simple explanation for the AMD smoothness?
Just plain old sw/drivers and not hw related at all?