After decades of typical IOR masthead rigs, we bought our present boat which is fractional. We've owned her for 8 years and 40,000 miles now... and I'm still not really sure how to get max drive from the mains'l! And yes, these are mains'l driven boats and getting it trimmed right does make a difference.
Things I have noticed:
The main needs to be much flatter than I expected, even in fairly light breeze.
It needs to be trimmed more inboard than I expected.
With swept-back spreaders, one can't get the main out as far as you might wish downwind, but it still seems to go pretty well wing/wing.
Controlling twist is important... airflow in the area above the jib
is different than below. I use telltales on the leech of the main and try to get them all flying smoothly (especially hard on the wind).
I'm sure that there are CFers who are better versed in this than I am... hopefully they will offer some better advice.
Finally, one would think that reaching in twenty knots and flat water
that you could exceed your theoretical hull speed
when everything is done just right. We occasionally get sustained 10.5 +/- 0.5 with our 44 foot LWL and a typically overloaded cruising boat (hull speed =~8.8).
Good luck and have fun