Just for the record, Ive done AMD and high end Nvidia cards before.
With the current generation of AMD Processors(Im referring to Phenom IIs) there seems to be a slight slowdown. Its not apparent at all in general use and only very rarley in games, but its there in the benchmarks.
Ive seen about a 50% bottleneck between a Phenom II 965 @4GHz paired with SLI 470s and a 1090T @4GHz paired with the same cards. The 1090t took the GPU benchmark scores WAY up.
and a 2500k @4GHz just blew both scores away.
There isnt a REAL issue, But do be aware that current Phenom processors just dont have the Integer or FLOPs to fully power a high end Nvidia card.
*Puts on flame suit*