I would think it would run at 30FPS for 3D, and split screen would be unavailable simply because this is already running below 30FPS all the time. So it would be 30FPS 3D (Division of the normal 60FPS into 30FPS for left eye, 30FPS for right eye). It wouldn't be as smooth, but it would still be better than split screen

I don't think I have the screen for that though, my screen is a simple computer monitor from a few years ago. Only 60Hz.