Hey, i currenlty experience a fair bit of lag on my 3 alternate clients when quad boxing and was wondering what would be the most limiting factor, i know its not a super computer and since im on a budget i would rather only upgrade a piece that would make the most difference

E6600 @ 2.6 ghz
4gb 667 Ram
8800GTS 640mb

Running the alternate 3 clients on 1 core of the processor seems to lag those down so im leaning towards upgrading the processor, however i almost max out on ram with 4gb and the graphics card could do with an upgrade, hence my post here as to what would be the best thing to upgrade