For racing, you'd want to go over the 9k mark to almost redline, because shifting to the next gear would put you back in the power.
If you shift at 9k, it'll put you lower in the rev range and not at the max power for the next gear.
On the street for "typical" riding, it's moot.
Knowing that 9k is max power and you're not getting more is useful just in the sense that you don't need to beat the bike to 11k all the time.
OK, I'm rambling.