See http://www.bbroleplay.co.uk/forums/showthread.php?t=6333&highlight=Smackaloaf for further emphasis
you really don't need more than 4 if your not gonna multigame and really push the comp. 4g is good enough.
With a high end pc more than 4gb isn't really noticeable. I don't even fully utilize my 4gb and I run everything on max.
I use Autocad quite a bit, and it's good to have more memory for that. It really speeds up the process.