RE: iSonic or Carve as Lightwind Board
I still think the Isonic 133 seems the best choice as it gives you probably 4-5 knots earlier planing than I think is realistic for your 104 liter board, but I think you will find the overlap you are looking for and may even find that you sail the 133 much further up into the 104's range than you imagined.
Again, if you really want to go for the "marginal planing" threshold, one of the larger Isonics (145 or 155) and a big 9.5 m2 + rig is going to be the right board, but what you gain in marginal planing, you are going to lose on the top end to some degree.
The 133 seems to be the best overall compromise here.
Hope this helps,