That was true in the past, but PCSX2 has improved by leaps and bounds since then. AFAIK, PCSX2 has had dual core optimizations for a while now. I can't tell you what speeds you'll get, as I am not interested in PS2 emulation nor is my computer even in the same ballpark as yours (needless to say, things go slow on my end, and I don't have a multi-core system to begin with). Sure, 2D games will run faster than 3D ones, in general.