Huh...
Thats twice now Tweaktown have had early reviews for Nvidia cards.
But anyway, the 660 seems to perform better than a 7850, but it will cost ~$50 more so that's justified. The review did end by saying that the HD7870 and GTX660 were ~equal, and they are at price as well.
Guess it comes down to how much you want to spend, and whether you prefer AMD or Nvidia. Still no word I can find on its release date either.