Well, i hope you know that you won't see much of a big improvement with those cards if you currently own a 4850. You could buy a 4870 or 4890, but whats the point? Wouldn't it be considered a waste of money to even have a "spare" videocard? And the 4850 is a fairly recent one at that. This is just my opinion, and just to let you know, by the time windows 7 gets fully released, dx11 cards will probably be released.
What's a "backup" card anyways lol.
Also, the 4890 is currently the highest-end single card ati has to offer, so im not really sure if it could be considered as a "budget" card. xD
