its better to look @ review & test it for ur self den just trusting wat dey claim.
usually v c all these claim to b performance improvement %, is based on "best case scenario", optimization for certain condition.

example, if the driver only boost 20% (max) fps on 1280*1024 wit no AA, den it is not any better for gamer who is using way higher resolution wit max AA.
but dis din't stop dem from claiming dat the new driver gives improvement of 20%