As a stand-alone card, GTX670 makes little sense at these prices. It's actually less than 10% faster than an HD7950 925mhz cards that cost $100 less.
(A) HD7970 is now faster than GTX670 is in Frostbite 2.0 games.
That includes winning in BF3:
1)
http://www.techpowerup.com/reviews/AMD/Catalyst_12.11_P...
2)
http://www.hardwarecanucks.com/forum/hardware-canucks-r...
3)
http://img.hexus.net/v2/graphics_cards/amd/HD7970/NS/BF...
and winning in Medal of Honor Warfighter:
http://gamegpu.ru/images/stories/Test_GPU/Action/Medal%...
(B) HD7970 is also faster in almost all GPU demanding games - Metro 2033, Crysis 1 / Warhead, Alan Wake, Sleeping Dogs, Dirt Showdown, Sniper Elite V2, Witcher 2 Enhanced Edition, Arma II games
(C) HD7970 has full voltage control and almost linear overclocking scaling with increased GPU clocks. What this means in practice is that it will take a 1280-1290mhz GPU Boosted GTX680 to match an 1150mhz HD7970, leaving GTX670 no chance.
(D) With 3 free games, you can sell the games you don't want making it an even better value.
(E) GTX670 performs worse in key situations involving higher MSAA modes and mods, for example Skyrim + ENB/Texture mods. For example in Skyrim with mods, HD7970 leads GTX670 by 20-23%:
http://www.computerbase.de/artikel/grafikkarten/2012/te...
In other words if you ever want to install mods, high resolution textures in other games like GTA V or dabble into Crysis 1 / 2 mods, HD7970 will once again win.
The main advantages a GTX670 offers are slightly lower power consumption, lower idle power consumption with 2 monitors and PhysX.
However, for SLI/CF you really need to have a case that has very great airflow to be able to buy these open air designs such as Power Color 7970 you linked or GTX670 Power Edition. In that case, it may not be a bad idea to go for EVGA GTX670 FTW SLI to exhaust the heat out of the case.
Alternatively you could really save yourself some $ and just get HD7950 and overclock it.
http://www.hardocp.com/article/2012/08/23/galaxy_gtx_66...
Get one of these. It's a way better deal than either the 670 or 7970:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Overclock it to 1100mhz+ and you are set, saving $100 over not wasting it on a GTX670/7970. At only 1.025ghz HD7950 is already nearly as fast as a GTX680 and good after-market 7950s like the Sapphire Dual-X, MSI Twin Frozr III or Gigabyte Windforce 3 can do 1100-1200mhz.
http://www.techpowerup.com/reviews/Sapphire/HD_7950_Fle...
Then next year, sell that card and upgrade to something faster so you don't have to deal with SLI / CF scaling issues.