Aprillia makes some good ones I guess. They also make a RS50 street bike, my wife owned one, it was so fun to ride.
Heres some pics, we paid 2800 brand new. Got a arrow exhaust on it. Went 60-65 with my fat rear on it.
Same motor! In europe they are hugely popular. I am not sure where you are from but here in New England we have Seacoast Sport Cycle, they are the #1 dealer east of the rockies, they can get and know all about modding the hell out of anything aprilia. The Creator of the "Clarkie" Tuonno is there race tuner there now. Aaron Clarke
Those 2strokes are really easy to deal with. Dump some oil in the injector bottle occasionally and go. As far as top speed I have no clue. And the go fast parts I am pretty sure readily available. There was the 95cc kit available for the bike(same motor) so I am sure there are plenty available.