both cards can be clocked to the same 1100+core/1500+mem. all new cards have locked bios with upped voltages. that being said, yes, at around 1125/1525 a 7950 will perform at bone stock 7970 levels.http://www.newegg.com/Product/Product.aspx?Item=N82E16814131478
at $250 the 7950 has a far better performance/price value.
if your going to be gaming on a single 1080p monitor, their is going to be no difference between the two cards as they both will be able to max out every single game to date except maybe crysis 3 where you can squeeze some higher AA levels out of the 7970.
i personally have an msi tf3 7950 at 1150core/1550mem on a locked 1.25v bios and i game on a single 1440p monitor and can max out bf3, ultra modded skyrim, bioshock, crysis 1,2... only crysis 3 has to be set to a mixture of medium/high for smooth performance. also at 1440p, AA levels can be dropped a little as most will agree the effect cant be seen