RE: wave sail size-ola,kevin?
Not Ola or Kevin here, but I thought I would offer some comment. It's interesting that your older sails are the same sizes I use, with the 4.2 being my smallest sail. For years I used to have sails in the 3.0 to 3.9 range, but with the outstanding performance characteristics of sails today, I find that I can sail a 4.2 in some pretty inside out conditions without too much difficulty. Also, it's my experience that sub 4.0 sails always seemed so twitchy and narrow in range, particularly on longer masts as Ola noted in his post above.
Regarding your one ideal sail size, I would have to say that a 5.0 would be my pick. Although a 4.2 comes in handy on real big days, I've found that a 5.0 offers the greatest degree of versatility overall. Most important for me is that I can use it very comfortably on 4 boards in my 5 board quiver, including my 100 liter slalom board. For most of the average higher wind days that I see in my locale and on travels, a 5.0 has without a doubt been my most used size. However, if I had to make a second pick, I think it would be a 4.7, but I wouldn't recommend going any smaller than that in the one sail scenario you're targeting. For some context, I weigh about 70kg.