I'm not one to give advice (never been on a racetrack!)
But I do make fast runs on a particular stretch of roadway now and again and I've noticed a tapering off of power from 6K to when the limiter kicks in at 8K. I believe it was Brian who has stated here that the peak of power is at 5K. When "going for it", I try to shift between 5K and 6K on each shift. It IS possible to develop an ear for the motor speed, but I'm not sure I could hear that surrounded by ICE noise on a track.
Yes - peak power occurs around 5k, and then you enter into a "field weakening" zone that attempts to maintain power up to about 8k. The power does start to taper off after the peak, but not so significantly as to say that it is always necessary to shift in a race condition. At a track, you often find (even on a gas bike) that you will run higher revs than you would otherwise run in order to not shift at an inopportune time on corner exit. Having the ability to "hang a gear" a bit longer with little penalty is what four-stroke, inline-four Japanese bikes do very well. The other option you have is to run a higher gear into the corner, trying to maintain corner speed and drive out with plenty of rpm window to work with.
Given his result, Bob probably got it pretty close to right to find the correct compromise - in this case, letting the motor over-run peak power a bit on the exits. An area where it might be possible to improve is on the straight, where you're really just trying to maximize your acceleration rate in a straight line. In this case, targeting a shift at 5-6k will ensure that you're getting the most of the power available.