The biggest competitor with the 670 will be the 7950 and the 660ti, The 670 is faster than the 2 but pretty close, if you want to save a few bucks get a 660ti or 7950. It also depends on what game you plan on playing in the future and other computer uses. If you plan to play a lot of games that utilize physx such as Borderlands 2 go for the 600 series if you like the extra effects nvidia brings.
A GTX560ti will be able to run almost any game really well considering your resolution. But im assuming you plan on upgrading to a full HD monitor eventually. So if you want to have a more future proof card go for the ones I suggested.