My HuaSheng49cc with Qmatic drive easily exceded 30 MPH during the last 'Dago ride with a 56 tooth sprocket.
It isn't even broken in yet. Top speed was 34 MPH on flat ground.
Now that the bike has a 60 tooth rear sprocket I don't know the top speed, but I did have it at 31MPH down hill with a tail wind.