Remember the brilliant RV770? This is history repeating with Nvidia as the one with the clever architecture.
GTX680 = Tahiti. So either card is worth buying in terms of performance. The reason to buy Kepler would be the better price, lower power consumption (i.e. GPU produce less heat energy), CUDA, fancy AA. As for features that were unique to ATI is also now available in NV, eyefinity and the lean/low power consuming architecture. I hope NV will never make another barbarian/joule guzzler GPU again.
This is really the perfect achievement from Nvidia! This is definitely a worthy buy, lets see if this will ignite the price war. I'll definitely get one when the price is a bit better than they are now.
What I seriously love about this card is that it is able to keep up despite being lean and consumes less power. Moreover, for once, this chip does not have a heat spreader like previous NV cards. This makes the job of adding water block a lot easier. When I mod my 560TI to water cooling, it was quite annoying that the spreader was in the way. I end up drilling holes and a whole lot of custom mod to get it to work.
The dynamic clocking system is a good feature. I actually tried my own custom dynamic clocking on my 4890. It worked but everytime the clock changes, there is a noticeable halt. This is similar to the problem faced by Kepler now. See the last paragraph:
http://techreport.com/articles.x/22653/9
Hopefully future drivers will fix this up because I hate those inconsistent framerate.