Have you got the 352.86 drivers installed? They were released just for Witcher 3.
I've got the game installed and patched now, so I launched it and got as far as the title screen, but TBH the opening cinematic was such turgid waffle that I didn't feel inclined to venture into the game itself
I'll motivate myself to do it at some point though. Maybe when I'm a bit drunk. Or have finished GTAV. The guy at work who's playing it has been regaling me with tales of what he's been up to and whilst he does really like the game he says it's very much an old-school RPG.
I'm still a bit bemused as to why I got it for free. I mean, I was already buying the cheapest GTX970 in existence, and on top of that it was reduced by £20 on a daily deal - so it wasn't exactly a tough sell. And yet I've got Witcher 3 which is currently £49.99 on Steam or $59.99 on GOG, and Batman Arkham Knight (£34.99 on preorder). So that's £85 worth of games on a £240 graphics card, most bizarre.