In my experiance a 560Ti (Gigabyte SOC 950Mhz) can play pretty much all games on highest settings with 30+ fps at 1080p
nVidia offers some advantages over AMD/ATI:
-Cuda
-3D Vision
-PhysX
plus nvidia cards often run quieter and cooler than ATI/AMD, well worth the upgrade. The only reason i upgraded from it was that i wanted to use 3d vision surround.