I went from 470's in SLI to a single 6950 (flashed to 6970) and enjoy gaming a lot more now. I know I lost a few FPS in most games, but it doesn't matter most the time, as I get enough. Mainly I like SSAA and MLAA which the 470's didn't have (the SSAA can be unlocked with Nvidia Inspector, but it didn't function as well). The main reason I changed was I absolutely hated the noise levels of the 470.
A word of warning, about 5-10% of those who unlocked the 6950 had damage or didn't work. There is a shader unlock script that has no issues with people. You might find that safer.