the FX paints do actually take a toll on FPS
Now, keep in mind the percentage of FPS loss to a normal brick is absolutely tiny
However, if you repainted Sylvanors Seattle with all chrome/rainbow/undulo and had the setting that handles FX (i dont know it off the top of my head, its been a while since ive played), you would definitely notice a lower FPS
edit; not taking into account that that isn't at all what AO is