Here's an article where they benchmark with different AGP aperture sizes. Thought it might be an interesting read since there have been some discussions about this setting.http://www.tweak3d.net/articles/aperture-size/index.shtml

Hello, Finally I hope this acurate article will clarify all confusion about disabling the agp/agp aperture size.Reducing agp aperture size is the key for + frame rateNever set the AAS below 16 MBAlways set AAS to either be less than or equal to your total system memory Martin

The results seemed pretty inconclusive to me. It would have been more meaningful if they had benchmarked more than 2 cards against more than 2 applications. If anything, I came away from this article even more convinced that AGP aperature may once have had a significant role to play in the early days, but unless you are running FS on an 8MB or 16MB video card w/ a 128MB+ aperture (and only 256MB of RAM), the impact of AGP aperture is somewhat moot.