I am about to upgrade my GPU i am not sure what will be my exact budget but let's say $100-$150 and it would be nice if you guys give me more than 1 option because i live in Egypt and not everything will be available, my current specs:
Asus Crossair III Formula Mobo
AMD Phenom II X4 3.4ghz BE 965
ATI 5770 Series HD 1gb (Oced @ 935mhz\1330mgz)
8 gb ddr3 rams
Windows 7 ultimate
You will probably not be able to get a card as good as yours within that price range.The best thing you can do is buy another HD 6770 or a HD 5770 (they are the same card) and use both the new and the old card at once (its called Crossfire).
Nope performance would be same if their the same model (example if both are 7750 they'll perform the same, but if one is a 7770 it'll be better; the higher the number for the same series, 7xxx or 6xx, the better the card). Just the factory OC would be slightly difference. Personally I prefer Sapphire over the other two with Gigabyte being my second choice but any would be okay.