it would be better to have 2x2Gb, a 'full stack' stresses out the mem controller and will effect overclocking.
make sure you use a 64bi OS though or you'l end up losing a lot of ram as 32bit can only see about 3-3.5GB. and GX2 will also effect how much ram your systems sees. so dont turn into the incredible hulk n throw the pc out the window when you can only see a little over 2.5Gb if you boot up with a 32bit os.
if you plan to keep this old rig on the road. especially for a gaming machine then it would be wise to upgrade the ram n get the most out of it before it eventually gets too slow for anything else but Warcraft.
but as it is - it would run most MMORPGs no problem but you dont play them games so it doesnt matter
“I used to be a serial upgrader like you, then i took a downgrade to the knee” -FreedomEclipse