The scale difference between concert & soprano really isn't all that much. A couple of inches. I don't have any problems going back and forth between them and don't think it would necessarily be an issue.
You can strum as fast on a decent soprano as you can actually strum. (I'd think that string tension has more to do with it than scale. A higher tension will make it easier to strum fast because the strings would be moving less than looser strings.) The limits there are your physical ability not the ukulele.
If the version of Super Mario Brothers you want to play doesn't require more frets than the soprano you've want to play it on, you should be fine. (And if it does, it's certainly possible to rearrange the song to work for the one you do have.) How difficult it would be to play depends entirely on your skill level, not the scale of the instrument.
