I've had my K-Pipe (190cc motor) up to 71-72 before I backed off, with the original 125cc, top speed was 58, (63 down an 18% grade) The frame was not designed to go much above 60, by the time you hit 65, the spaghetti forks are softening, 72 was downright scary, I feel it has the capability of going close to 90 at the rate it was still accelerating. I have since replaced the stock rear shock with a gas YSS, I have a steering damper, but not yet mounted, and looking into having my local machine shop fabricate me a fork brace as well as getting some springs for my weight, wound.
not that I am a speed freak, my preferred speed is 35-45, not even in top gear, some destinations require riding in highway speed traffic