GTX680=GK104

The demo ran on a 2-way SLI setup last year, not 3-way. The third card was used for GPU-PhysX. This time, FXAA was used (instead of MSAA?). Also no info on fps. And a year of time to do optimizations. And GK104 has double the computing power (not performance!) of a GTX580. So it's plausible, you just have to think critical.