Well, if you insist, then the 680 will work yes, but unless you are running multiple monitors or at a resolution above 1080p you wont need 4gb of VRAM, the 3GB in the 7970 is more than enough. Also, I take back the triple slot remark, it would appear that the 4gb version is the only DCUII cooler that is not triple slot from Asus, odd.
That cooler is what I have and it keeps the temps down, make sure to get another fan for it and use a push/pull setup. Here's a video that'll help you overclock, you always test with a program like Prime95 for stability, though usually anything below 4.5GHz on an Ivybridge chip is good to go: http://www.youtube.com/watch?v=IAnjq6W-UCk&list=WLBF4EE36B5367C758&feature=mh_lolz
This system will be good for maybe 3 years, but games won't still be running at max settings by then, in fact, high resolution monitors are probably going to take over pretty soon with 4k tv's coming down in price and becoming more common.