I'm a purist, so I run everything at its original resolution and aspect ratio. Also this is why I bought an arcade monitor for my cabinet. The only thing that won't be as originally intended is vertical games running vertically on a horizontally mounted 4:3 monitor, but I can deal with crop bars on the sides to keep the original aspect ratio, and I'm going to build another cabinet with a vertically mounted monitor next. Who wants to play Donkey Kong all stretched out like that anyway? I know Mario is fat, but good grief.