Depends what resolution you're looking at and which titles. This usually is the case anyway.
So from my point of view HD6970 is between GTX480 and HD5970 (though closer to first). I'm gaming at 1920x1200 and sometimes use two monitor setup. Besides the titles I have planned to try over Christmas are exactly the games where Cayman gains the most. To name few: Metro2033, Stalker, F1 2010, COD, ME2, etc. I also will need to finish Dirt 2 which gains a bit on new card from AMD.
PS. Almost forgot about GTA IV I had on hold because my HD5870 1GB was running out of VRAM when settings were set to max.