5750 or 5770?

well what are you planning on using this computer for? what's your monitor resolution? what's your budget?

actually take back the resolution question i have an lg w2253tq so i'm going to assume 1080p. But if your just going for raw horsepower and don't care about budge go with the 5770

As Jonny indicated it depends mostly on what resolutions you want to play at and and what games you play.
The cards are a very similar value and similar technology. The 5770 costs $30 more and is proportionally more powerful. So if you have the money get the better 5770.

EDIT: but make sure your power supply is strong enough.

Niether. 4850 or 4850x2.

@ Happyjesus: 5770.
My i5 750 is running one at 1920x1200 with few problems but I seldom use more than 4x AA at such a high resolution, if you want the full eye candy the 5850 is a better, if rather more expensive, choice.
BTW if your MB supports CF at 8x/8x dual 5770s' are a devastating combination, if not for now, then for the future  .

Yeah, you'll want an HD5770 for that resolution.