An overclocked GTX 780 can match a GTX 690 already.
Proof? See these two articles side-by-side:
http://www.hardocp.com/article/2013/08/14/galaxy_geforce_gtx_780_hof_edition_review/
http://www.tomshardware.com/reviews/catalyst-13.8-frame-pacing-crossfire,3595.html
Compare the average fps results for Crysis 3, Far Cry 3, Metro LL, and Tomb Raider.
Crysis 3: GTX 780 OC = 44.6 avg. fps / GTX 690 = 39.6 avg. fps
Far Cry 3: GTX 780 OC = 50.2 avg. fps / GTX 690 = 82.4 avg. fps
Metro LL: GTX 780 OC = 65.0 avg. fps / GTX 690 = 69.3 avg. fps
Tomb Raider: GTX 780 OC = 55.7 avg. fps / GTX 690 = 47.6 avg. fps
The GTX 780 OC loses to the GTX 690 in Far Cry 3, ties in Crysis 3 and Metro LL, and wins in Tomb Raider. I realize the settings used in both articles aren't identical, but they are close enough for a reasonably fair comparison. Keep in mind that a GTX 780 is a SINGLE GPU card and yet it is doing battle against a top-of-the-line dual-GPU card.
Finally, at $689.99, the overclocked GTX 780 sets the bar that AMD has to beat:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814162142
Will AMD bring out a comparable single-GPU card? They'll be in trouble if they don't.