560 Ti is the easy choice if ya have $200 to spend:
Guru3D uses the following games in their test suite, COD-MW, Bad Company 2, Dirt 2, Far Cry 2, Metro 2033, Dawn of Discovery, Crysis Warhead. Total fps (summing fps in each game @ 1920 x 1200) for the various options in parenthesis (single card / SL or CF) are tabulated below along with their cost in dollars per frame single card - CF or SLI:
Strongly suggest buying a factory overclocked version for two reasons:
1. Just about all of them have oversized coolers which help you get a pretty good OC over and above what the factory provides. MSI, EVGA, Asis, Gigabyte, XFX, Paliit fit this category
2. About 1/2 of them have improved PCB's with beefed up VRMs of 7 phases or more which allow extreme overclocks. Asus DCII TOP, Gigabyte and MSI Hawk fit this category....the Twin Frozr has only 6 phases.
Here's an example of what 7 phase VRM and oversized cooler can do: