For best performance you want to run 2 sticks of ram = this way it runs in Dual channel.....
With your current setup, your not getting the full memory bandwith your mobo/cpu/ram can provide....It's not currently in dual channel....
I don't know what your finances are like, but adding a second 1GB stick along with 2x 512 sticks will be pointless....your not going to need or use that much ram..
If you can afford it, get anoth 1GB stick and run 2x 1GB sticks in dual channel, mayby sell the 2x 512 kit to pay for it! -> this would give the best performance...
Running 4x sticks of ram with the current amd cpu's causes the cpu to set your command rate to 2T -> command rate is another one of those timings....but it's an important one....going from 1T to 2T will hinder performance more than changing from CAS 2 to CAS 3!!
Most people won't notice this kinda thing though......
It's upto you if you wanna spend the $$ for this.......I suppose you do, simply beacuse your a member of a tech forum and are asking the question ;P
SO -> my suggestion is sell the 2x512 kit and run 2x1GB in dual channel!
Would I be better off choosing just the 2x512's or just the 1x1GB dimm?
Running 2x512 will be better than 1x 1GB stick
I don't know if you can get 1GB sticks of PC4400 ram....but the G.Skill F1-4000USU2-2GBHZ PC4000 ram will hit PC4400 speeds...
I just got mine today (40mins ago)....currently running @ ddr500 speeds
I'll see how high they can go after dinner...;)