2 unlocked 6950's in CF or a 7970/GTX 670 ?

Hey guys,

So basically I'm tired of my crossfire setup. This cards are awesome when they scale well, but a lot of times they don't. There's too many headaches with the drivers with crossfire support, the microstutter gets annoying, and it gets a little toasty in my rig. I think it's about time that I upgrade. I play at 2560x1440 on ultra high settings in most games, so I really push those cards to the max. I am currently playing games like BF3, Skyrim, GW2, and Borderlands 2, and obviously I want it to be futureproof for the next year at least.

Okay so my questions.

1.) First off I would like to know if it's worth it to pay some extra cash to upgrade. I know there will probably be a performance loss, but there will be less headaches I have to worry about. Do you guys think that's it's worth it to upgrade to a single card setup?

2.) How much do you think I could get off my cards? Like $150 each? Would they sell? They're in great condition, and both are unlocked.

3.) How much of a performance loss would there be going to a 7970/670? And finally, which of these cards is overall better. Would it benefit me to go with the 7970 because I play at such high resolution? Or is that eyefinity I'm thinking of? I want the card more future proof, and pulls ahead in most games.

Thanks so much