CPU is the biggest performance hit thou, both PCSX2 and GSdx are limited by the CPU at some point, sure u can get a better card but most of the times it only means u can run higher settings without performance hit, while running a faster CPU will enhance both the limits pcsx2 and gsdx have making it faster overall
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Main Rig: Pentium Dual-Core E2160 @ 2.8GHz -- 9600GT @ 715/1033MHz -- 4GB DDR2-667 4-4-4-12 -- Windows Server 2008 SP2
Collecting dust: AMD Athlon XP 2600+ -- ATI Radeon 9500 Pro -- SB Live 5.1 Digital -- 2.5GB DDR 2-2-2-5 Ram -- Windows 2003 server r2 SP1