-dxmode70 or something. I don't know the actual command, but it's something like that. Do a search for running it in 8.1, and whatever -command you see, substitute 70 for 81
Turn off 2.0++ in the advanced menu. Set it to 2.0 and you go from 15 FPS to 70+ with no change in graphics, aside from the shadows looking slightly different. Best tweak evar.