RE: Help with board
I'm not a team member, but I thought I would offer some thoughts from my perspective.
Given your situation, I would recommend concentrating on a slalom board in the iSonic line. While full on slalom boards offer somewhat of a greater initial challenge, I think that payback in the end would be more satisfying overall, particularly when considering the flatter water conditions at your locale. Although a valid argument could be made for some of the other models, such as the S-Types or Carves, especially since your sail focus isn't centered on fully cambered race designs, I'm of the belief that friendlier no cams (or even wave sails) will still allow you to extract the extra performance characteristics of a full up slalom board. Without question, you will be able to find better windward performance. Moveover, you would be able to fully tap into benefits associated with higher aspect fin designs normally matched to slalom boards. Personally, I would never be without a least one slalom board.
Regardless of your final direction in the end, picking the right sized board will be a crucial consideration. Sailing fresh water conditions makes it all the more important to have enough volume to give you a viable slogging capability. Yet, because your sails are on the smaller side, one would have to question going with too much volume. All things considered, I would recommend targeting boards in the 110-115 liter range. If you were to open to the benefits possible with larger sails, it might be of value to consider a higher volume board in the 120-125 liter range. But, if you're firm in your resolve to stick with smaller sails (6.2 and down), I would doubt that a higher volume target would offer tenable results.