Actually, the weight (mass) does not affect top speed much. It is mostly wind resistance (aerodynamic drag) that matters when it comes to top speed, and just as important, range.
Weight affects accelleration and uphill speed.
For best top speed and range, something like Craig Vetters fuel economy bikes would be the solution. Maybe based on the rolling chassis of a 125 or 250 single. Narrow tires give less rolling resistance and less wind drag.
https://craigvetter.com/pages/470MPG/470MPG Main.html