Rob,
I'm using the Slingshot system. Lots of good information on gear and windsurfing foiling here:
http://www.foil-academy.com/courses/wind-foil-academyWith this system, one starts on a shorter mast (14") and then progresses to longer masts.
My goal is to be able to windsurf in light mountain winds with a big board and small sail. (J bay, DC).  I'm totally amazed that in sub 20mph conditions that the big, fat, heavy Starboard Go can get on the foil with a 6.0 m sail. Dubock has a Hyper 135 that we may try. A deep Tuttle box is needed and probably best. Dave at Windance has an adaptor to allow the gear to fit a regular Tuttle box.  I would probably not try to attach the foil to other kinds of boxes.
The ride is like skiing in deep fresh pow.
One cool thing is that the gear can be aggressively sailed and pumped more downwind than normal because once its on the foil it heads almost directly upwind.  It may be that staying downwind is the challenge.