I'm not sure if this is the problem, but the Radeon HD4x00 series puts a good deal of it's load onto the CPU, and this is apparent in PCSX2, where the program itself needs the most of both cores, so you end up with one and a half cores for PCSX2, and half a core being taken by the GPU (or thereabouts for PCSX2, if I remember the graph runawayprisoner posted)
Still, I can't see it causing that sort of drop.
Is the dual core option enabled?
Try testing his video card in your system just to see?
Still, I can't see it causing that sort of drop.
Is the dual core option enabled?
Try testing his video card in your system just to see?