I dont think you would see a bottleneck with the 560Ti, but probably you would with the 570 and higher. I dont think it would even be much with a 570, and probably would depend on the game. The gtx580 would be held back by your cpu, unless you could over-clock it.
Tom's Gaming CPU Hierarchy Chart shows your cpu in the same class as a PhenomII 945 or so. Have you considered the GTX 560Ti 448 core model?
It performs above a 560Ti and slightly below a gtx570. That seems about like a pretty good match for your cpu. Here is a few of them to look at. http://www.newegg.com/Product/ProductList.aspx?Submit=E...
So you're saying that my processor and memory right now has no problem and will not bottleneck any of those cards shown in the link?
And yes, i've only really used nvidia but i could open my eyes on amd, i suppose i just havent really researched about amd that much compared to nvidia cards.
I personally run a 570 and the only game i struggle with getting 60fps maxed at 1080p is Metro 2033 (about 40ish with every option turned on and up to max). I agree with GI, throw a mild overclock on your cpu, replace your psu and possibly add another 4GB of RAM and whatever the best card you can afford is.
Yes, I feel for the most part that anything beyond the 560Ti 448 core is a waste, and you would probably have to overclock your cpu to around 2.8-3.0Ghz to actually get 100% usage on this card, at least in some cases. Either the regular GTX 560TI or the 448 core seem about right for a balanced system in your case.
True..the resolution does matter, but at the most common...say, 1600X900 to 1920X1080 range the 560Ti or Ti448 core should be a good match for the op's cpu. Below that resolution range the cpu would become more of a bottleneck, and above that range..well I think both would struggle in very new games like BF3. Of course there is varience from game to game, and resolution to resolution, but in general it seems anything below the 560Ti level would create a graphics bottleneck, and anything over a 570 would create a cpu bottleneck. That leaves the 560 TI...the 560Ti 448core and the 570.