50cc just isn't a lot of displacement for carrying around a 200lb. person. I should know -- I am one, and I had a Yamaha Vino 2-t 50 for years. The 2-stroke is going to have more get-up-and-go, but unless it's liquid-cooled, not all that much more.
If your aversion to a 125cc is legal in nature, I would suggest that you try to get the legal issues straightened out, and then move up to a scooter that can actually get you where you need to go in a reasonable amount of time. I live in a decent-sized city, and the Vino still got me across town faster than the bus, so it was always a win for me, even at 37mph top speed.
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