It's a known fact that a slower CPU uses MORE resources to do the same work. You just proved it. Maybe you should try listening to the people you're asking rather than arguing with them at every turn. People like you, I point to Dell.com and give up.
A GTX 590 is faster than a 7970. The 590 is a dual GPU card. So it's obviously going to have a higher fps. The thing is, you are starving it with a 3Ghz CPU. It's fact, we don't make this stuff up! Clock speed scales well with a card like that. You think you can handle it with no bottleneck but I'll tell you what. A 7970 is a touch faster than a GTX 670 at stock, and a GTX 590 is faster than both at stock. I had a Q9550 @ 3.8Ghz (that's 800Mhz more than you) and my FPS jumped significantly when I upgraded to my current system with a 4.5Ghz 3570k and I kept my GTX 670 the same. Read my post I linked below, it will prove it to you. If you ignore this then I know you're not here for advice at all and simply want to argue all day about stuff you obviously don't understand.
http://forums.anandtech.com/showpost.php?p=33521789&postcount=1