Yeah, it seems like ATI really rushed their drivers. They were falling behind the GeForces in Doom3, and they wanted to stay competitive so they hurried to write drivers and released some pretty shoddy ones.
Anyway, I think the 4.9 driver only gives you a significant benefit if you have one of the really new models of ATI cards (newer than the 9800 Pro). Downgrading to 4.7 shouldn't cause a difference in most games.