Problem is the GTX670 at the "same money" you refer to are most likely with reference cutdown PCB and piece of poo blower cooler, rather than a proper full size PCB with a custom cooler.
I recently bought a 120Hz monitor, so I'm probably due for an graphic card upgrade soon. As much as I would like to go back to Nvidia (since from my own experience I feel that they can actually deliver smoother gameplay despite lower in fps figures), I don't think I can justify getting a GTX670 over a 7950 (if I was to buy a new card right now), purely because of the GTX670 has a narrower memory-bus, and also more expensive. However, if there was a Asus/Gigabyte GTX670 with a full size PCB and custom cooler for the same price as a 7950, then I might be tempted even if it means going for 256-bit memory bus over 384-bit.
One thing i can say is that the 660WF i have in my PC atm is a lot better then the 7850s ive tried ive had both MSI and WF 7850s and they are crap compare to the 660!!
AMD cards spike fps all over the place, this 660 doesnt and it has much higher fps in all games ive tried.
One thingi should mention is that the 7850 was being a pain in the ass in my machine so im not sure if its down to that and therefore it underperformed in games?
Im gonna try AMD again since im getting a new machine but i hope its as good as Nvidia or ill be ****ed! I have 0 problems with Nvidia cards, some say thats why they are more expensive, plus the other extras like physx, i dunno how the hell AMD cant do that its nothing special :|