You have it backward. A lower pitch is equivalent to a HIGHER rear end ratio. The pitch is the distance the prop will travel through water in one complete revolution, assuming zero slip. 24P moves 24" in one revolution. A 26P moves 26". Which is the same as a lower (numerically) rear end ratio as the wheels spin more given the same # of driveshaft revolutions. To raise RPM, you decrease pitch. This will improve hole shot, but just like the 4.10 rear end, will lower top end. To go faster, you raise the pitch, which hurts hole shot but increases top end speed. You want to prop the motor to turn near max RPM when the air is cold, dry and dense. IE not summer. If you prop it for max RPM in the summer, you will be blowing over the rev limiter when the air is cooler.
The Pro XS has a redline of 5750. You want to get close to that. But surprisingly, quite often LOWERING the pitch will improve top-end, because as you get up into the power band of the motor (5500+) it makes more power which will then increase the RPM even more giving you more speed. I don't know much about a Z8, but a properly propped 200 Pro XS ought to at least reach mid to upper 60's, even in a very heavy boat.