ram question

[Theory]

i kinda cheaped out on my ram when i bought my computer. so i wanna buy some better stuff so i can oc my computer. this i what i got:

MB CHTECH VNF4/Ultra NFORCE4/ULTRA - Retail (Qty=1,Price=$73.00)
CASE ASPIRE| XINFINITY BK 420W RTL - Retail (Qty=1,Price=$55.00)
CPU AMD 64 |3200+ ATHLON 64 939P RT - Retail (Qty=1,Price=$152.00)
CORSAIR D400 512MX2 VS1GBKIT400 R - Retail (Qty=1,Price=$79.55)
and i have a bfg 7800 gt

can i put just slide that ram over to the other 2 slots and buy some better ram like 150 or more for ram. i would wanna know if it has to be the same company ram or u can have 2 different kinds and if 4 512's are slower than 2 512's?

im gonna get a better proccessor i think too. my computer isnt what i had hoped i guess. it runs all the games but not as good as i want. do u think some good ram will make bf2 run like butter, it runs good but i want it to be over the top.

 

[AtomicSpark]

If you mix ram, it will run at the slowest speeds. Not sure if it's wise to overclock ram, unless you know what you're doing. If you want any "speed" increase you'll have to lose your old ram and go with something faster. You not only have to consider the memory speed but the latency too. I haven't checked lately what the new top of the line speeds are but mine seem to do pretty well. :E