AnandTech checked out ATI's Catalyst 5.7 drivers which were released last month. They didn't just compared performance on one card, no, they checked out the performance difference between the Catalyst 5.6 and 5.7 drivers on five different cards: the X600 128MB, X800 XT 256MB, X700 PRO 256MB, X700 128MB and the older 9700 PRO.
As you can see with the x600, there are some significant gains here. The most notable is with Half-Life 2 at16x12 with AA, which increases by exactly 25%. FarCry at 16x12 without AA goes up by 20.2% with Catalyst 5.7, and probably would have shown to increase even more with AA enabled, if we could have ran the benchmark..