Thanks again for being so helpful. You have a great attitude of helpfulness.
Let me try to answer your questions.
My lake is about one mile wide by one mile long. There is only one place to launch. In a southeast wind, if we go out half a mile we get better wind. But usually when the wind is from the SE it is good enough that I can plane on my 120 and one of my four sails. A more common direction is NE, and in that wind the wind does not get stronger the further we get from the launch. So I think you would say a longboard is best.
You asked how often I go out and want to sail in 5 to 10. Not often. Maybe once or twice a month. (I sail about 70 to 90 days a year, so once or twice a month is not often for me.)
Let me ask you this. It has been years since I sailed a long board. When I did, I wasn't as good as I am now on shortboards and at planing. My big fear is that I might find long boarding boring. Can you please comment on that.
I really do love to plane, but I don't want to buy another short board if it is only marginally better than my 120 (keeping in mind that I really don't want to have a sail larger than 8.5). So I am torn between going for an Isonic (as Belskorpio suggested) and planing on marginal days or going for a long board and enjoying cruising. I wish I had more money and a larger van--sure would make the decision easier because then I could buy both an Isonic and a cruising long board. Anyway, my question is this: I know a long board cruises nicely in light winds and will work fine with an 8.5. But will an Isonic 117 Wide be a big improvement over my 120 or just a small improvement? Thanks in advance.