I built my rig a few years back (Intel Core 2 Duo E8500, Asus P5Q Pro mobo, Radeon HD 4870 1GB). I can't remember the exact RAM but CPU-Z tells me 4GB Dual DDR2 with a DRAM frequency hovering around 400 MHz. I feel like tinkering with the rig a bit and thought a good addition might be additional/all new RAM. What advice would you give? What would provide me with a noticeable difference in performance?