The thing is that 640x800 going to each eye, with a wide angle fov and this device so close to the eyes, you're going to get a lot more visual fidelity than if you were staring at a 640x800 mobile device from about 6-8" from your face. This is because of how the optic nerves work. It's too complex to explain without breaking out the equations and a lot of scientific jargon that will make mere mortals weep. But maybe John can explain it better than I can - especially since he's more of a graphics guru than most of us devs who develop graphics engines for video games. All in all, I don't think the resolution is going to make one lick of difference.