The main point of the break in is to seat the rings to cylinder wall. Little bits of metal will get scraped off until the seal is close to perfect. To a lesser extent this will also happen in the bottom end and the transmission. It is essential to do this right away. Race teams break in their engines on a dyno at high power settings, but they never let them get too hot. If the combustion pressure is too low during the break in, the rings will never seat correctly. The result will be blow by during the life of the engine. You will know this has happened if the oil gets dirty quickly after an oil change. That engine will never deliver best power and will suffer a shortened service life. In addition, dirty oil full of combustion by-products will be lubricating the transmission and clutch. Does that sound like a good thing?
The first 30 miles are critical. Let the engine warm up, then take it up to 70%-80% power (5,500-6,500) in 1st gear and hold it there for 5-10 seconds. Then bring it back down to just above idle for 20-30 seconds. Monitor the engine temperature. Now repeat the process in 2nd, 3rd, and 4th gears. Use 5th and 6th gears for your cool off periods. Obviously you need a good place to do this. An uncrowded freeway can work pretty well. After 30 miles of this, change the oil and filter. This will get rid of all the little bits of metal. After this you can run it to full power occasionally until it has about 100 miles on the odometer. Change the oil and filter again. The rings will now be properly seated and you can ride it any way you like from now on.
Why does Yamaha not recomment this? Why do none of the manufacturers recommend this? Ask their legal departments. "Yes, Judge, I was busy monitoring my gears, time, and temperature while wildly variying my speed, just like Yamaha told me to do, and the next thing I knew I was in the hospital." No wonder they tell you to go slow. I used to break in bikes strictly by the book... never again. I always ended up with slow, oil burners.
Incidently, the high power break-in method is required by all manufacturers of piston aircraft engines. I know there are differences. I don't even want to think about the BMW guys and their unique ideas.