If you can get to 57mph then you are doing far better than most on here, i cant see how you could get it any faster without towing it behind a car
Most struggle to hit 50mph wihout a big bore kit. I only average 45-48mph and i have the same set.up as you almost apart from the leo vince. Take it you fitted a larger main jet anyway?
What variator do u have? What size belt? Or is belt stock?
If i ever got to 57 i would be more than happy, in fact i would be amazed. 51-52 is.my record.but that was.down a long hill using 7.5g rollers. There are a few guys on the forum running 70 or 80 cc kits who only get 50-55mph so if your speedo is correct then you are well over the scooters limitations really. When you say it was downhill you got 57mph, it wasnt a vertical hill was it? i.e, a cliff?