The SMS got an amazing port of RR. And there are games on the 7800 that kinda give you a glimpse of what RR would look like on the console. Fatal Run has the hilly roads like Road Rash has, and FR runs really smoothly too. Maybe those of you that know the inner workings of the 7800 have some idea of what a RR port would look/run like.
That sprite sheet says it's from the arcade version of Super Hang-On. Those sprites have 9-10 unique colors each, so on a 7800 they would most likely need to be scaled down to one of the 160 modes on a 7800 because that's where the colors are. likely the same would be true of the Road Rash graphics and the end result might look more like the Game Gear version than the SMS version, which isn't necessarily the worst thing ever:
Every head-on driving game on the 7800 us