I have a Derbi Atlantis and right out of the box it could run away and hid from most "Mopeds" and that is the straight up truth. I have a 76 PUCH w/a 70 cc kit. Which by the way is pretty good in the proformance column. But the un mod.Derbi out performed the modified PUCH hands down. I recently put a Terrigas high proformance exhaust on it. For a less than 50 cc scooter/moped, it'll hold its own w/an older 2 speed Vespa.
However, guy, my question is why does it have to be a MOPED and fast as hell. Unless you are into racing, which you are not or you wouldn't be asking this question, why a MOPED that is fast as hell. After all, isn't that an oxymoron. Now here's the scoup on speed as in going fast, your only limit Dude is $$. More money equaltes to higher performance equipt. which equates to SPEED. But on the street, in real life takes precedence, speed & mopeds "ain't worth the trouble or the money" because some Duphious on a medoicre small dirt bike or motorcycle is going to wipe you in a race or in ease of crusin (You can't take a chix crusin on a PED can you?). Also racing peds just don't hold up, after each race they have to be rebuilt. If you live thru this dream and are lucky, you'll only up broke and back to using shoe leather express, but smarter about how you spend money. it's your choice.
Rich ( I learned it the hard way)