All of these choices look good. You should definitely go with the 7970, hands down. You can either buy a GHz edition which will actually perform better out of the box for less money than a 680, or you can buy a vanilla 7970 and overclock it yourself.
The 680 is, sad to say, a waste of money. Even if you wanted to stick with nvidia, a 670 will give you very nearly the same performance for a lot less money.
Yeah, I'm kind of leaning that way...that way been the 7970. But I really need to find the best way to spend that remainder of the budget to try get best bang for buck. I know the Matrix 7970 is about $480 which is cheaper than the 680. But if you got any more advice, I'll be glad to take it on board.
cheers for the reply though:-)