What memory should I use on my GA-P35C-DS3R Rev1.x board?

Looking For:
-High Performance/Gaming Memory
-800mhz
-1x2GB or 1x4GB

System To Be Used On:
-GA-P35C-DS3R Rev.1.x
-Intel Q6600 @ 2.4ghz (stock)
-2x1GB GEIL PC2-6400 800mhz DDR2 (GX22GB6400DC)
-Windows XP Sp3
-500GB Seagate 32MB 7200rpm
-Palit 8600GT Sonic + (oc'D from 625->705mhz core clock 900->950mhz memory clock) = XFX 8600GT Professional Series

Goal:
-Have a system total of 4GB DDR2 800mhz RAM
I know it wont show all 4GB since Im using a 32bit OS

Options:
-Keep the old RAM. Add 2x1GB High Performance Memory
-Replace the old Ram and add 4x1GB or 2X2GB of 800mhz High Performance Memory

Memory Brands Preferred:
-OCZ
-Crucial
-PNY
-Kingston
-GEIL

Again I have to take into consideration the board I am using. The order will be online and as much as possible I dont want to send it back due to compatibility issues. Please help me choose the right ram based on the information I have given. Thanks!