BIG POST:
All numbers are for 1920x1200 with the same graphics settings and same rig
GTX 480 1536 mb
5970 2048 mb
--------------------------
Bad Company 2
GTX 480 - 55
5970 - 74
5970 up by 34.5%
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Far Cry 2
GTX 480 - 84
5970 - 86
5970 up by 2.3%
--------------------------
Tom Clancy's HAWX
GTX 480 - 114
5970 - 136
5970 up by 19.3%
--------------------------
Modern Warfare 2
GTX 480 - 135
5970 - 130
480 up by 3.8%
--------------------------
Anno 1404 dawn of discovery
GTX 480 - 71
5970 - 105
5970 up by 47.9%
--------------------------
CoD: WaW
GTX 480 (1536 mb) - 92
5970 - 84
480 up by 9.5%
--------------------------
Crysis Warhead
GTX 480 (1536 mb) - 51
5970 - 61
5970 up by 19.6%
--------------------------
Just Cause 2
GTX 480 - 76
5970 - 65 (driver issue, multi-gpu didn't activate)
Fault, but
480 up by 16.9%
--------------------------
Mass Effect
GTX 480 - 120
5970 - 177
5970 up by 47.5%
--------------------------
Brothers in Arms: Hells Highway
GTX 480 - 109
5970 - 123
5970 up by 12.8%
--------------------------
Resident Evil 5 (Dx10)
GTX 480 - 121
5970 - 143
5970 up by 18%
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Out of 11 fairly modern titles, the 5970 won 8 times with an average margin of victory of 25.23% FPS. When the 480 won, it won by an average margin of victory of 10.07% FPS.
Source:
http://www.guru3d.com/article/geforce-gtx-470-480-review/16
Unfortunately, as stated by Jryan, the 5970 is a dual GPU card and it isn't quite a fair comparison from that perspective. HOWEVER, it is fair in the fact that it's the strongest single PCB solution that each company offers, and thus ATI still owns that crown. So it depends on your point of view on the matter.
In the end, numbers don't lie, and number's state that the 5970 still remains the strongest single PCB solution for your GPU needs.