It depends on how high you want the resolution to be. Is 4xIR in Dolphin enough for you? Then the GTX 660 would be enough.
PCSX2 + custom shaders (FXAA, HDR, color correction, etc) at 5x native resolution usually runs perfectly with my GTX 760. If I try at 6x native + shaders, it isn't enough powerful for some games that are very GPU dependant. The worst example I've seen is Shadow of the Colossus. I sometimes hat to use 3x native to get over 60fps (without speedhacks).
In my experience, Dolphin usually needs more GPU power. Maybe because its internal resolution is higher than the one the PS2 uses, so when you multiply it by a high ammount (let's say x6), you end up having a higher resolution. Example: native in Dolphin is 640x528. 6xIR(3xIR+4xSSAA)= 3840x3168 pixels. 46.67% more pixels than the usual 4k resolution. In PCSX2, native resolution is usually 512x448 (depends on the game). So 6xIR= 3072x2688. At 6xIR, Dolphin uses 47.32% more pixels than PCSX2 at 6xIR, so it needs more memory bandwidth and more GPU power in general. That's without having into account if Dolphin games are harder to emulate in the GPU or not.
PCSX2 + custom shaders (FXAA, HDR, color correction, etc) at 5x native resolution usually runs perfectly with my GTX 760. If I try at 6x native + shaders, it isn't enough powerful for some games that are very GPU dependant. The worst example I've seen is Shadow of the Colossus. I sometimes hat to use 3x native to get over 60fps (without speedhacks).
In my experience, Dolphin usually needs more GPU power. Maybe because its internal resolution is higher than the one the PS2 uses, so when you multiply it by a high ammount (let's say x6), you end up having a higher resolution. Example: native in Dolphin is 640x528. 6xIR(3xIR+4xSSAA)= 3840x3168 pixels. 46.67% more pixels than the usual 4k resolution. In PCSX2, native resolution is usually 512x448 (depends on the game). So 6xIR= 3072x2688. At 6xIR, Dolphin uses 47.32% more pixels than PCSX2 at 6xIR, so it needs more memory bandwidth and more GPU power in general. That's without having into account if Dolphin games are harder to emulate in the GPU or not.
CPU: Intel Core i5 4670k @ 4.4GHz
GPU: GAINWARD GeForce GTX 1080 Phoenix "GLH"
RAM: G.SKILL Ripjaws X DDR3 16GB 1600MHz CL7
OS: Windows 7 Ultimate x64
GPU: GAINWARD GeForce GTX 1080 Phoenix "GLH"
RAM: G.SKILL Ripjaws X DDR3 16GB 1600MHz CL7
OS: Windows 7 Ultimate x64