I found the 6870 to be a good bang for the buck they also work good in CF. However, I have always run CF and almost across the board it is more trouble then its worth. I like my 6950's and you can always reflash to 6970.
From my research if you do plan on using CS6 alot you probably should go with a Nvidia. Its true that price per dollar amd is better; however, Nvidia still makes more powerful cards for the most part. The difference is often small but still there. Here is what I found.
What I couldnt find is how much faster CUDA is quantitatively compared to none CUDA, but that last article says that CUDA will sometimes result in better quality.
Basically you should do some research you would be rolling the dice a bit by going with an AMD. The advantages of CUDA might not matter much for you based on what your doing or your patience. Also a good overclocked CPU will help pick up the slack.
In any case, I would probably say go with Nvidia. http://www.videocardbenchmark.net/high_end_gpus.html
That link shows the stats for many cards and the 560 ti or gtx 480 are good buys. However, alot of people say the 480 runs hot so I would say if 200 is your price range go with the 560 ti. But dont take my word do your research.