RE: Fast Medium wind board for heavyweights
iSonics 133 and 122 and ST 137 are the most likely candidates from those families. 12-25 is quite a wind range in board sizing terms, so if you'll be spending the majority of your sail time at one or other end of the reange, it would be worth tilting the choice/compromise a little more in that direction. iSonics have a little extra efficency, which always helps in the case of heavier riders, whereas the ST's easier going style makes for a more relaxed big board technique once the conditions are powered - and choppy.
Try and get a test ride / demo on the iS133 (or 122), that should nicely benchmark both the ride and sizing expectations.
Cheers ~ Ian