I think the speed issue is mostly "done" at yamaha. I'm not exactly on their R&D team or anything, but I've done a good bit of research, comparisons, graphs etc. to get over myself.
FIRST let me clarify - If you have to ask why you want to go fast, then you'll never understand. Some of us are just speed nuts. We like going fast even if for a few seconds just like you may like getting up on your wake surf board, or doing the latest mod to your boat.
You have heard time and again that the pumps are the limiting factor. No one really knows WHY and many have tried to analyze it to death. I've gone and analyzed it from the opposite direction. What has the speed result been with extra horsepower? What are other jet pumps doing? Is there an efficient point of the pump? How does it compare to other brands? (sea doo, hamilton, berkely)
Long story short, the current 155mm pumps are at a great spot with the 180 hp 1.8's. They are in a great efficency range and the motor has enough torque to do your sports. If you put 250 hp to them, you need to upgrade the pumps, which yamaha did for the waverunners. They bumped it to 160mm and gave a better vein design. They realized the same thing I did. For a comparison, a Hamilton pump is stated that it can take 350 hp and is 210mm. This is a ratio of approximatly 1.6 Yamaha reaches this same 1.6 point with a 155mm pump at 258 hp. I don't think it's a coincidence that they upgraded their pump at that point.
The power/efficiency curve starts to level out pretty quickly at 200 hp and you are overcoming the pump limits by throwing more power at it. Sea Doo also uses 155mm pumps, which is again why it takes 500+ hp to go that fast. Scarab is supposed to have those same twin 255 hp engines and when I was at the Chicago boat show, the guy showed me pictures and and texts from some big shot that sent him info about the 24'. He stated he was doing 65 mph. I can maybe believe it if they upgraded as well to the 160mm pump.
Yamaha has obviously made the decision to make an AWESOME boat but more on the luxury side. The scarabs look more like a fancy toy. I actually prefered the Glasstron ones as they looked much more sophisticated, but they won't be having the twin 255 hp engines either. The fact that Yamaha is addressing issues here is just awesome, and I'm sure it will continue.
Hopefully this is what the compitition does to Yamaha!