if you have the money just buy the better faster single gpu, less heat, less power draw, and overall better performance. as for which one, they are about the same, the 680 will run better in some [strike]occasion[/strike]situations (I should proofread what i type sometimes lol), while the 7970 will do better in others. both easily OCable, just make sure you have a good psu to support them and you choose the one you want, no point in letting someone talk you into something and you be dissapointed, look up benchmarks if you are really serious about which you want to use.