Well, that's no rocketscience, you want to keep the revs in the max power range. When i shift at 6000, it drops to about 5100/5200 in the next cog, close to the max power again. When I would shift right before it bounced off the limiter (say, 6500), the revs would already be past the max power point when the next gear drops in, hence making you go slow.
Capiche?