Going back to your mouse issue, thats a bit strange though. I have a 770GTX that works well with 3 screens, but asking my 680 to do the same causes a noticable drop in performance - and thats only just under the same price bracket. Your asking it to essentially work on 2 x the resolution so I would be looking no less than the £300-400 price card bracket. Multiscreen generally only really works an the really high end cards effectively. I also prefer cuda as it enhances things like photoshop processing, which I use a lot. I know its a copout but I never went back to ati/amd after my last card driver update caused no end of problems.
Get an nvidia card then, if they don't look into the issue for you. Some still don't write exclusively for 8 though. Indeed - but modern drivers no doubt have generic win 7 + 8 compatibility.
