my friend it is hard to say it depend on games and what resolution are you playing at?
by the way your system is good enough i am sure with every game you will be getting more than 30fps with maxed out.
I am using a Q8400 @3.8Ghz and a single gtx560ti. In BF3 ultra I am getting an average of 30fps with highs of 48 and lows of 19 (thus high setting for me for smooth gameplay) 30fps is the minimum for a real smooth gameplay a higher fps would mean that when it gets to a low point it wont be as low. but I do prefer playing with 45+ fps. With your faster processor and SLI then you should have at least 60fps on average there but im sure there would be a few dips.
I game on a Core i5 760, 8GB Ram, GTX 570 SC and in BF3 multiplayer I get in the average low 50s (minimum around low 40s) FPS @ 1080p with 4xAA, 16x anisotropic filtering, ultra textures, and the rest set to high. If I turn everything to ultra I get in the low 40s on average, which in my opinion is too low.