It depends on the resolution they settle on. The test systems they have now are very low resolution, but I believe they plan to have 1080p in the final version. That means you'll need a system capable of hitting 60ish FPS at double a 1080p resolution (3840x1080). That is because the system has to render a frame for both the right and left eyes. Rather than flipping a single display back and forth between the left and right eyes, like active stereoscopic 3D, it displays images to two separate screens, so it isn't exactly 120hz, but it is two times 60hz.