Coolest mini-bike I've ever been exposed to was Bonanza's (MX-1510?) Mini-Motocross. My brother had one and I was once clocked at 65 mph on it. Man I was stupid back then, no helmet, no protective clothing, dirt road. Supposedly, it would do 70, 0-50 in less than 6 seconds, and sounded like a chainsaw on steroids. An expansion chamber with no spark arrestor hiked it's Hodaka Ace 100 engine to 11hp, 5 speeds, manual clutch. It ended it's years when the back wheel broke, my brother then bought a Hodaka Ace 90 motorcycle with a trashed piston as a donor frame from a buddy of mine and installed the motor off the MX. The MX frame was then discarded. Of course, if we knew then what we know now, It would have been saved. Last I saw of these bikes online, somebody wanted 10K for one.
I've always heard the Speedway bikes with the Sachs 125 were even faster, don't know if they were quicker, God help the rider if they were. Because keeping the front end down in any gear was a chore on the MX.
Looked exactly like the one in the link.
http://www.strictlyhodaka.com/images/bonanza.jpg