I have the EVGA 6600 GT and am pleased, easily worth $170.
However, Something might be onto something
Quoting the far cry tweak guide
"Lighting Quality: This setting determines the quality of light interactions with the environment. At Low, surfaces don't show any sheen from lighting, and most lights emit a relatively dim unrealistic glow. At Medium the situation hasn't changed greatly, with surface textures still not having any noticeable shine or sheen to them. When set to High, the lighting greatly improves and reflects off appropriate surfaces (such as metallic floors) with a nice shine and depth. Your flashlight and all lighting give off a bright glow (depending on your Special Effects Quality settings - see above). Very High appears almost identical to High, except using Very High will ensure you're using Pixel Shader 2.0 (highest image quality). The higher this setting, the greater the impact on your FPS, especially on slower machines."
So this guy is saying that Far Cry, on ultra high settings is using PS 2.0
My specs are listed below in my sig, my PC does not run far cry on ultra high settings.
I guess you might use PS 3.0 and get decent framerates if you do some very serious overclocking....