HD4850>HD5770 - the former is faster
HD 5770 newer than HD 4850 - it supports DirectX 11. You'd be better off selling the 48** and getting a single HD 58**
What? Umm, no. The 5770 is easily stronger than a 4850. Unless you meant Xfired 4850's > 5770.
A single 5770 can handle just about anything at 1680x1050. I would just go with the 5770 for now, with a future intention of Xfiring two of those because thats stronger than a 5850 then.
Sorry, I meant Xfired 4850's^^^ although in games, framerates are simliar (with each card being a single,
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I just need answer: 2x HD4850(because its going to be very cheap and I already have one) vs. 1x HD5770
and dont worry about mobo.