Flybywyre,
There is no reason to go over 1Gb for gaming. I do not even know of any games that use 512Mb of RAM.
After 512Mb of RAM, adding more RAM will start to slow down the computer. A simple way of thinking about it:
If all the memory addresses are listed on a sheet of paper, it is a lot easier to search 1 sheet of paper than it is a whole book full of pages, to find a memory address.
The trick is to have enough RAM to keep the computer from offloading the information it has in its RAM to the Hard Drive, 1Gb is more than enough.
(I would love to see the full specs of the system you are thinking of building.)
Take Care,
Richard
P.S. Every thought about going with an Athlon64 Platform if you really want gaming performance on an extreme edge?