Nvidia could easily come in with mid end cards faster than the stock gtx780/ti. They would just be clocked silly high and have no headroom. The review's would look good and they could price high as well. The reality would be once you overclocked the gtx780/ti they would be faster once more. Nvidia are great at marketing and i am sure they would sell.
Reminds me of the 480 vs 580. Similar performance but the 580 ran allot cooler.

. The 760 is a bit more sensibly priced now anyway. You have to remember that the 670 was only the same price as the 760 for a few weeks whilst all the old stock was cleared out. The 760 came out slightly above the 660's launch price and nowhere near the 670's launch price.