Marc,
For reference, I ski in Colorado. In my mind there is no reason to hammer it around the island, in fact you lose speed when doing so. Next time you are out, try it, the speed will drop. Once you are in this situation, where the throttle is down, and your speed is decreasing, you're in a lot of trouble at high altitude. At lakes here in Colorado, I've found that keeping the boat at approx 28 and throttling up at the backside of the island is more efficient. You will find, with practice, a more efficient way to get to speed by throttling up at the backside of the island at the right spot and from the right speed. Honestly, I do not understand why drivers drive so fast at the turn around with or without an island, its not necessary in my opinion!
Out of course driving is just as important as in course.