The graph talks about power delivery, it suggests the power drops off after 6k revs, my car makes it's peak power at just under 6k revs according to a couple of dyno's I've had done previously. The power doesn't just die at 6k revs, it's still there, just not as accellerative as it was when it was on 3k revs, but it should still be quicker to rev to the red line before changing up because of the gearing... a lower gear will always accellerate quicker than the next gear up, unless the torque difference can compensate for it in the next gear... I still think the car is quicker revving to just before the limiter before changing up, unless you was in say 4th gear where the car hasn't enough torque after 6krevs+ and will do a better job in 5th(where it's legal to do so.)