well a here's a great example. The 7950 pulls an average of 42 FPS in W.o.W and drops into the 20's at times on full settings.
I throw in the GTX 660 (non-ti) and enjoy an average FPS of 56 with a minimum in the high 40's.
This was in new content of the new expansion of Mists of Pandaria. I recorded for 60 seconds with Fraps to get my results. The games looks better and more defined witht the Nvidia card.
All settings on ultra at 1080p.
However, I must note, Starcraft 2 looks better with the 7950. For example, When I warp in a pylon while playing protos it is much more defined with the 7950.
Please note, I am not a fan boy. I don't think there is a clear "Black and White" as one brand better than the other. For example on paper, the 7950 specs make it the superior card becuase of the memory size and bandwidth, however I have verified a game can perform better with the GTX 660. Being superior isn't just in the physical components of the card, it also includes drivers and how well the card processes a game with the available resources it has.
I acutally like both cards for different things. Just feel AMD is not currently maximizing their resources right now. The 7950 was a Christmas present. I was able to grab the GTX 660 (non-ti) superclocked edition at a local store for $209.