FWIW, I was able to pickup a high end 27" iMac at the Apple Store (Fort Worth TX). I7 3.5 GHz/8GB Ram/780M/3TB Fusion is the standard build, upgrade to 16GB Ram and was on my way.
Bought the same iMac last week. Runs really well, lightening fast. I'm playing the new Batman Arkham Origins (admittedly through Boot Camp) and it's running with ALL settings on full and the highest resolution poss. Quite impressed!!