Hobie, I could talk for hours about all of this. Your questions are all valid and I have dissected all factors ad nauseum. Slayer and IFSH's responses are what I expected to hear and confirm some suspicions I have. The suspicion being that there is under-performance with my outboard rather than it not being strong enough outright.
I'm pushing a 16 ft. aluminum Fisher with a 50HP Mercury EFI 4 stroke. Without typing a book, some key tests are that I cannot get this boat fully on plane at Eleven Mile when I am alone with a 9P 3 blade prop. I neglected to mark down the RPMs but I'm guessing that they were around 5.5K and barely touching 20MPH. I also ran the boat alone at Blue Mesa alone with a 7P 3 blade prop and could not rev limit the RPMs.
Obviously, when I start adding people things go downhill from there.
The boat has a hydrofoil, but that seems to just change the angle of the hull to allow for the least water resistance... while not on plane. Boon and I took the hydrofoil off at Willies with the 7P prop and it was a disaster... no hull angle control.
My brother and I got the boat up to 23 MPH on Chatty last year with no gear, and he is my size. The outboard starts instantly and idles well. I have changed plugs, fuel filter, and have a new primer bulb coming in the mail. I see people at these lakes with more people in their boats and smaller motors on plane...