What browser are you using? If Qt one, like Opera or Konqueror, you can almost get rid of slowness by running this command:
nvidia-settings -a InitialPixmapPlacement=0
I have it in my .xinitrc and "screen painting" problem didn't disturb me anymore.
I'm using RGB subpixel AA with 'cleartype-like' patches from David Turner.
Forget to say, it's not working with Xgl/beryl