There's your bottleneck. Your CPU. Honestly, RAM isn't going to help you as much as replacing the Duo. I would tell you to just try and upgrade the CPU, but the socket it sits in is dated as well and getting a Core 2 Quad isn't as cost effective as just buying a new i3/i5 board. But hell, if you've found your setting sweetspot then don't spend money you don't have to. If you can just drop the resolution a touch more and that stutter should smooth out. Happy hunting, mate.