Which sail should I use today - why not ask your iPhone? SailSize, a free iPhone application, lets you enter your weight and the current wind, and calculates what sail size you need to get planing.
Calculations should be accurate since they are based on James Douglass' sail size spreadsheet. Available for free at the iTunes store. (And no, this is not an April Fools Day joke!)
I've been windsurfing for more than 30 years, although this includes several multi-year periods where I did not windsurf at all. I got really hooked again a few years ago, after getting married to my lovely windsurfing wife, and starting to take ABK clinics. ABK also introduced us to windfoiling, which then led to winging. We mainly wing and windsurf on Cape Cod, with regular trips to places all over the world.