The problem with 7950 vapor x is the unlocked voltage complaints in many of the cards,the dual x is a better option.Also the gtx 660ti performs a bit better than a 7950 at resolutions up to full hd even with full anti aliasing.It gets defeated only in the 2500*1600 and above resolutions where it's less memory bandwidth becomes a problem.
Not aware of the complaints with hd7950 vapor x.You can go with other custom versions of hd7950.
HD7950 in most of the games perform better than gtx660ti @FHD.
According to many reviews during the release of gtx660ti,gtx660ti fares nearly as good as the hd7950 but most of the comparison takes place with a stock hd7950(800MHz).
Even with new bios patched to the reference hd7950 will take the lead.
GALAXY GTX 660 Ti GC OC vs. OC GTX 670 & HD 7950
In this review both gtx660ti and gtx670 are clocked around 100MHz higher than hd7950 but still hd7950 comes out on top technically.
AMD Catalyst 12.11 Performance Analysis
In this review you can see mostly that hd7950 is ahead of gtx660ti even before the newest performance driver.
As far as skyrim is concerned even before the latest performance driver and latest bios patch,hd7950 performs better than gtx660ti with performance difference increasing in favor hd7950 once you apply more AA.
*i.imgur.com/sBvyY.gif?1 *i.imgur.com/S5jGy.gif?1
The thing is that at 1920*1080(without AA) there is a small gap but once you have AA added to it then a good amount of gap is there in favor of hd7950.