Well I originally was going to sell the HD7970's and buy the new GTX 680's off of New Egg. The bad news is New Egg sold the cards to me and then ran out of stock so they said " We can put you on a waiting list"
I told them heck no. But I found someone (Locally) who wanted to do a trade.... my two HD7970's W/Water blocks for his GTX 680's. I did it and have my new water blocks (For the GTX 680's) on the way. He was newer to water cooling (So blocks were already installed for him) and he was more into Eyefinity so it was a great deal for both sides.
In comparison.... looking back there are some things I really like about the GTX 680's compared to the HD7970's but there are somethings they lack too.
On average the GTX 680's yes are faster then the HD7970's but in real life tests not by much!
Also when you factor in Nvidia's new offset clocks it's not always a for sure thing to keep the clocks you are shooting for.
Example* You could set your offset to be 1250Mhz but because of built in thermal throttling the cards will down clock to an approved Nvidia Temp. Sure there is a work around but it is still not a for sure thing.
When you set the HD 7970's to 1300Mhz that is where it stays.
Nvidia's clocks are a more for sure thing if someone was using Water cooling or NO2 but for someone using Air anything that raises the cards temps above Nvidia's approved 70c the cards will throttle down just a little. You can raise the GTX 680's Power limit to by pass this a little but again I will stress these cards will down clock if they go past Nvidia's approved temps.
Now there are some nice things about the Offset feature. *Example* your GPU's are not constantly running at such high clocks burning them out quicker. It also saves power. Also I have noticed that with the Offest feature the top stock speed for these cards is not 1056 it can actually be higher but it ranges from card to card. As long as the card is under the approved temp and the card needs the power.... the GTX 680 will continue to clock up. Just like it mentions in this thread at another site....
https://www.evga.com/forums/tm.aspx?m=1516486&mpage=1&print=true The top speed for my cards for example is 1124Mhz Stock (If it needs the performance and stays under Nvidia's temps)
Maybe I should write a review as coming from someone who has owned both cards. But right now.... I would say I really do like them both equally! And anyone with a HD7970 thinking of upgrading to a GTX 680..... If you really want to go a head otherwise in terms of performance you won't get any real gain even in bench marking.