You may or may not benefit by changing the aperture size.
Default setting is 1/2 your installed RAM,but that doesn't mean that's the best setting for you.(or anyone else)
I've 256M of RAM installed but it didn't make a difference for me changing it to 256M, 64M or leave it at 128M.(a few months ago i've tried it before after reading a review, and that guy did benefit a lot,but it didn't work for me. (it was on a gamers site can't recall wich one))
The only way to find out if you might benefit changing the aperture size is doing it.
Run something like 3Dmark2k (at least 3x looped for a good average)shut down, wait a few minutes (let your pc cool down),then change the aperture size and run the same test,
(Write down your results) and see if it does make a difference.
Here are my results running 3Dmark2k 3x
64M aperture size ---->4750
128M aperture size ---->4753
256M aperture size ---->4759
OK i agree,it seems the bigger my aperture size the better(?) my results are,but it might be the other way around when i do this test again running it 20x or more.
Just give it a go.