Officially? No. Un-Officially? Ya. Not much different than the 5xx series. From the limited time I had with it, there seemed to be a wall where the larger amount of cache started spitting up errors. The errors didn't crash it out, but the benchmark's increase wasn't linear with the speed increase as it was with modest speed bumps.
This was a 650, but maybe the 660 would do better with it's higher skew...doubt it though. I'm all about FSB speeds more than core speeds, so dropping the multiplier is fine by me as long as it drops the core back under that error wall.