When unlocked the HD6950 will be a minor upgrade in terms of average performance(5-10%) but it has a number of other advantages;
As a single GPU card it won't have any crossfire scaling issues/microstuttering/minimum frame rate issues.
The 2gb of memory will help performance when maxing out the settings in the latest games at high resolutions
DX11 compatibility for the current and future games that use those features.
Eyefinity for using up to 6 monitors at once.
Greater power efficiency, especially at idle, which also means less heat to deal with.
MLAA which is a post processing AA that can be used in games that don't allow for traditional forms of anti aliasing.
Much improved crossfire scaling if you ever do want to add a second card.
More current A/V features.