There's so many bug fixes listed in the release notes of this version that
I don't doubt they broke new things fixing all that stuff. I'll wait for
6.6.
Also wouldn't be surprised if the 'Adaptive AA' they've introduced for
older cards causes an instant performance hit if they enable it by default
for those cards.
My thought on the subject would be that they allow more image quality
to down grade the gaming experience and by this getting people to buy
new stuff.
It's just like putting more detail in the option tab it require more
power from the graphic card. I remember once changing from an older
version of drivers and then notice that the image quality was less
details and by that increasing the fps.
In example in oblivion if i'm ok, there less grass going from 6.4 to
6.5 but i cloud be wrong and its not what i smoke. (little joke
here)...
Plus it is said on ati web site that on some older card that it can
add more fps going from 6.4 to 6.5 if i'm ok. Ie: up to 30% more of
fps in ut2004. I wonder where they cut in the rendering on those
cards. Maybe on the number of object that appear in games in a certain
distance.