Does the GeForce GTX 670 Spell Trouble For AMD?

After many months of talking up its latest architecture, Nvidia reclaimed the single-GPU performance crown with its GeForce GTX 680, which outpaced the Radeon HD 7970 by about 7% in our tests. Kepler's arrival forced AMD to slash prices across its Southern Islands lineup, including a $70 drop on the HD 7970, putting…