Does anyone know of a way to get HDMI video to display a 4:3 image (“pillarboxed”) without taking a severe performance hit? Using “runcommand 2” seems great for Genesis, it seems, but it makes (some?) SNES and NES games unplayably slow. NES – Bubble Bobble was the first one I tried, and it was painful. I tried 1943 and Contra, and they displayed similar slowness.
You could set your pi to output at 480p 4:3 but then for some reason it cuts about 5% off the image at the top and bottom. You could (what I do) set the pi to 720p then change the runcommand.sh to 2 and overclock the pi to 900Mhz which should stop any slowdown.