Just posted an hour ago...early 670 preview/benchmark....looks pretty close to 680 and as suspected, only missing 1/8 of the cores and a little clock speed.
http://wccftech.com/nvidias-gtx-670-previewed-benchmarked-early-launch/
I calculate between 90 and 99% (mostly 92-93) of the framerates of the 680 based on the tables....but that seems weird with only 87.5% of the cores AND a lower clock speed. meh....guess we'll have to wait another week to know for sure
EDIT: That article was a summary of a tweaktown article. Here's the source article:
http://www.tweaktown.com/articles/4710/nvidia_geforce_gtx_670_2gb_video_card_performance_preview/index3.html