Here's my race bike I built for the motorized bicycle races (which are often frowned upon by moped guys because it's not a "traditional" moped.)
24" bmx frame stretched and modified for a V1. Weighs just under 70lbs and geared for the track will hit 55mph. (10-42 gearing.)
Posting it so you get ideas to think outside of the box. If you're building your own frame, you don't have to conform to "but it's not a real moped" mentality.