Yeah, I used to hit the high beam indicator on my Honda Metropolitan with a nice downhill. I figure that was 50 mph. On level ground, it was more like 46 mph. However, that was a liquid cooled machine that probably made more power than most 50 cc 4T engines, coupled to a Polini variator with a taller top ratio. I usually rode WOT, and I probably got a few cops scratching their heads at the silent stock yet cute scooter blowing by rather quickly.
I also demoed a Kymco Agility City 50 4T with the overkill 16" wheels for my friend post-derestriction for Canada because I weigh next to nothing. I got about 40 mph. I have no idea how your Super 8X 50 4T motor relates to said Agility City though or what its jetting looks like.