Recomended *intel E8500 3160Mhz / AMD X2 6400+ 3200Mhz (some games need even more CPU power to run fullspeed, like Tekken 5 ( C2D E8400 OC @ 3800Mhz) ) *2 GB RAM *Nvidia 9600GT / ATI 3850
PCSX2 won't take any advange of Quadcore processors cause the emu works just with 2 threads, PCSX2 loves high clocks.
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*try GSDX 1.4 for DBZ BT3!! use it!
*for other games use GSDX 1.9 SSE2 (SSSE3 or SSE4 if is capable on you pc)
*if you have graphics problems with GSDX (like emu crash on Gran Turismo 3/4), try ZeroGS 0.91 ..if the problems continues, nothing to do, just wait for a new release.
*you have to find your better emu config for each game on your system. (try lower resolutions,Vu Skiping,Frame skiping, etc.)