Rather than focus on how to make a video scale better (which is highly depended on the codec, game engine, and up scaling method), I'd focus on what "wrappers", mods and patches are available to _improve_ the game, if needed, and then re-record at each resolution using a macro or some other automation for the game play (so each video is as identical in execution as possible). Games are a moving target, and even very old games, if still popular/fun, get occasional love to keep them working. So showing new videos of what is currently available is more interesting to viewers than what was possible previously (except for comparisons, of course). (A good example is Might and Magic 6, which was pure software 3D, and only with the MM6/7/8 merge mod can play with hardware 3D at modern 16:9 4K resolutions--which made me replay it recently for nostalgia and to see what it could have been if not limited by technology of the time.)