Hey, i'm a pretty avid BF3 player and i used to run FRAPS alot to see the FPS variance just before i upgraded.
I went from a PhenomII X6 1100T @ 3.8ghz to a 2500k @ 4.4ghz (all other settings the same), with Ultra settings @ 1080 I DID NOT NOTICE A SINGLE FPS DIFFERENCE IN 64 PERSON MP with my 670 GTX. It was really disappointing to say the least, but definitely a learning experience.
People were talking about how i'd notice a jump in minumum FPS, that's complete BS! I didn't notice any difference at all with Ultra settings (still dipped to ~30ish FPS when alot of crazy stuff was happening, but avg is 60fps and it was the same with my X6).
in OLD RTS games(Dawn of War 2) i noticed a jump in performance for sure. But even modern RTS games like Shogun 2 fully maxed out i hardly noticed any difference at all, real shame but it just goes to show alot of people on these forums that advocate how one CPU is better in higher resolutions with completely GPU dependant features turned on (like AA & ultra quality) don't have a clue what they're talking about.