I must have missed this one yesterday in my slumberous mood. The boys over at Tweak3D have an interesting article discussing AGP Aperture sizes. For those who have ever asked me what the best setting is, why not click the link below.
Some people think that the more RAM you share with the graphics card, the larger the performance boost. In some cases, this might be true. In others, it might result in a performance drop. There are two common outcomes from setting the AAS too high: (1) If you share too much RAM with your graphics card and an application takes advantage of that, you will have less RAM for other functions of the software, and possibly for background applications. (2) If the graphics card does not utilize the memory, it is not taken from system memory. In this case, there are no problems with AAS sucking all of your system RAM, despite its setting in the BIOS configuration utility. The latter is the most common case, since most people have enough memory now to compensate for a high AAS, and most applications would not take all of the memory anyway.More information at Tweak3D