The 5750 is a very light card for your resolution. You will be able to play games at lower details, but you certainly won't be cranking up the eye candy in Crysis. You would want at least a 5850 to get a good gaming experience at your resolution. Here's a combo deal that would be great if you can stretch the budget a bit:
Depends on the GPU, and if you want to Crossfire later.
Antec is pretty good, but most people tend to recommend the Earthwatts models. Also, note that the bigger OCZ I listed is cheaper after rebate. Or this 700W one is the same price. Both of these are good quality units.