When you compute rpm, stock gearing, and stock tire size you get a theoretical mph.I took it to 154 a month ago, and I remember the rpm and gear that I backed off.
Today, on my way to work, I noticed I was in a higher gear, and slightly lower rpm, and I was going 20 mph slower.
Gear changing from 5th to 6th, you lose about 2,000rpm. So figuring the numbers stay roughly the same, 10k rpm, in 6th, is about 12k in 5th.
5th at 10k is 102 mph while 6th at 12k is 133 mph. Also the other thing that throws people off is that they are not true with themselves when getting a high speed rpm and mph. The rpm needs to be held constant for a few seconds so you are not accelrating still. The best explanation of this is this. Try and launch very very hard. accelerating all the way through your rpms. when you hit your max rpm look at your mph. Now slowly run through your rpms and look at your mph at redline. It will be way different mph wise.