The 670 and 7970 perform basically the same at stock up to 1080p resolution, trading blows depending on the game.
http://www.techpowerup.com/reviews/MSI/GTX_650_Ti_Boost_TF_Gaming/26.html The 7970 most likely will OC better (and has way more compute power http://developer.amd.com/resources/heterogeneous-computing/opencl-zone/ ),AMD Eyefinity Technology
http://www.amd.com/us/products/technologies/amd-eyefinity-technology/Pages/eyefinity.aspx Bitcoin mining
https://en.bitcoin.it/wiki/Mining_hardware_comparison the 670 gives you CUDA
http://en.wikipedia.org/wiki/CUDA PhysX http://www.geforce.com/hardware/technology/physx/videos# TXAA http://www.geforce.com/hardware/technology/txaa/videos# FXAA
http://en.wikipedia.org/wiki/Fast_approximate_anti-aliasing ADap. Vsync etc and lower power draw. Both are solid buys.If you still can't decide which card to take try looking at the games that you play or specific features that you want.If cost really matter to you then you might want to go with whatever is cheaper to you. HardOCP did a full review on adaptive vsync, was impressed with it if you want to know further details about it: http://www.hardocp.com/article/2012/04/16/nvidia_adaptive_vsync_technology_review/3