Do you have a gear chart? I have one I can send you in an excel spread sheet. With just 3,000 more working rpm the bike will produce 20 MPH in top gear 15 MPH in 4 or 5 th. My dune/hill shoot port job that TRO73 has will produce the 3,000 more rpm on the top end compared to unported stock cylinder. So it can be done without changing gearing or tires. I've done it.
The gear chart is good to have if you don't have one. Its a working sheet that takes all the multiplication out of your hands. You can change gearing and tire size with it.