I agree, good discussion and a fun thread. I hope others take something away from it that will be either helpful or inspirational.
In Dallas, Texas, we get good winds October - June, then the three months of summer pretty much "suck" for windsurfing. Summer is when the formula board comes into play and gets used quite a lot.
This year has been exceptional in Dallas for wind. I will be out today in 15-25 knot winds for my 49th sailing day since Jan. 1. We have 5 days in a row with the same forecast, but it's HOT. 103F (39.4C).
No need for formula today, but I did go out on it about a week ago in 5-20 knot winds with a 9.2. When the weather is hot, our winds are EXTREMELY VARIABLE. On a few 1km reaches yesterday on a 5.0 sail, I would encounter winds ranging from 5 to 20, to 10, to 25, to 15 knots. You can watch/see the dark patches of swirling wind on the water moving towards you, so it keeps you on your toes. Other times you may plane on relatively steady winds for some distance, jibe and then slog all the way back. It's a pain, but better than staying at home.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.