I'd suggest ya wait 2 weeks and find out instead of guessing how they will compare. In recent years I have followed 2 rules of thumb....
At system cost < $800, look to an AMD build
At system cost > $800, look to an AMD build
At GFX card cost < $200, look to an AMD card
At GFX card cost > $200, look to an nVidia card
Last generation, nVidia sold more 560's(10.25% of cards hitting steam servers) than all 68xx and 69xx AMD cards combined (10.15% of cards hitting steam servers) . AT the lower market niches, AMD similarly cleaned nVidia's clock.
The 670 "carpet bombed" the high end market including the 680. The mid range is still up for grabs tho nVidia coming awful late to the table. Right now I have lotta builds on "standby" waiting for the 670 TOP to become more available and the 660 Ti to hit shelves.