Sounds like you need more prop to push RPM's up to the max -- around 5750. A 26P should get you close (400 RPM per pitch, so you should be between 5600 - 5700). Also, I'm not sure how removing 4" of setback will affect overall speed & performance, perhaps others on the board can comment, my first take is that doing so will have a slightly negative impact on performance, although clearly having the hydraulics should offset this.
The tempest is an excellent prop for this boat, so I wouldn't change that unless you want better handling & holeshot (but sacrificing 3-4 mph) -- then go with the Trophy Plus...
By the way, I am running the 10" fixed with a 200 Opti on the 901, and am running at 70 -- do you have a lot of driving experience? One of the most common mistakes made by drivers has a major impact on speed; most guys get up on plane, then tilt / life their engines to full speed operating position immediately. This doesn't optimize the prop and the motor's thrust. Rather, you should ease up in increments, allowing the boat to reach its top speeds. I'll usually make 3-5 adjustments once out of the hole...
Hope this helps,
David
