Is there a definitive word on how high/low to set agp aperture, et al?

Question

Seemingly, the most elusive part of the bios settings is the agp-related settings (agp aperture, fast-write, etc.).  I say this, because all I ever find on posts is 'this is what I do', or 'well, this is my rule-of-thumb...'.  Is there no definitive logic for how to set these?  I realize, like some people say, you can futz with the settings, run a benchmark, rinse, repeat, until you get your best benchmark setting, but this seems a bit too 'random' for my taste.  I'd actually like to understand what I'm doing, why I'm doing it, and be able to see the benchmark to prove it right or wrong.
Does anyone have a good, definitive understanding of these features to be able to offer a reasonable justification for setting them one way or the other?  So far, in my limited understanding, I tend to think I should set my agp aperture to as low a setting as possible, for example, as my video card has 256mb onboard, which exceeds the requirements of the games I play in-and-of-itself.  Thus, why would I want to tie up system ram when video card ought to have more than enough already?  Maybe this sounds stupid, but that's why I'm asking 

Answer 1

256Mb should be more than enough to run todays games at HI settings. From what I understand it only addresses out memory tasks when onboard memory has exceeded its amount. Running down the AGP bus to RAM would be slower than onboard because of the interface (GFX-upto 256Bit DDR3 etc). If the app can run happy with onboard RAM, the amount set for "aperture" is used for system use and is not set a side until the apps needs more than GFX can offer addressed onboard. It does need an amount set even if its the smallest amount. I thinks
Also please read below pages:
http://www.tweak3d.net/articles/aperture-size/
http://www.cybercpu.net/howto/basic/AGP_aperture/index.asp
http://www.anandtech.com/news/shownews.aspx?i=17139