If you turn down graphical settings that honestly make little difference on action games down you can run mostly anything. Stuff like AA,AS,shadows(on some games),number of decals and others are barely noticeable on games like BF or CoD but they really put pressure on your GPU.
I have a 6750 and by disabling or lowering the settings I mentioned above I can run pretty much any game i want including the ones mention by the previous poster with at least 40fps
No way it's better to play the first fear series cranked vs. fear2 that lags, same goes for cod black ops vs. the older ones,
Playing prostreet at max is better than dirt2 stuttering.
I have two systems, so not playing certain games is not the end of the world on the older pc.
My other computer is my gaming/htpc. It is a A6email@example.com with two sapphire toxic vapor-x hd-4870's, stock is 800/1000mhz, they are set at 850mhz core/1050mhz mem. It more than doubles the framerates at the same settings vs. the X2-4400+/hd-4870 750/900mhz system.
Also many of those games are on sale dirt cheap on steam vs. the newest one and look pretty good with the graphics cranked on high.
It is best to try out the playable demo first to see how it runs before buying a game too.