How big? Sail size for light wind

I have found sail size goes up exponentially to win another knot at the low end. I currently use a powerful 8.6 (turboGT) in 6kts with the formula and 1200 Lok? wing. In 7kts I can use either the 8.6 with a 1000 race wing, or my 7.0 with the 1200, but on the JP135. The 7.0 / formula combo flies a little later. In my experience, a bigger sail than 8.6 doesn't get me flying earlier, but does help to keep flying in the lulls.

From about 10kts I can fly with 4.8/JP135 or 92L/Lok?1200.

Since 9.2 is the biggest for foil racing, why not use your 9.5?
If you can handle it for Formula, it'll work fine for foil.

I had a Severne 9.5 I tried to foil with. The issues I found was the size of the sail also increased the weight. Regardless, I found that the gusty winds also made it a little rough to handle once I was in the air. I found a better balance with an Ezzy Cheetah 8.0. The lighter rig made it almost as effective with the Severne 9.5. Not quite as powerful, but once I figured out my pumping technique, the 8.0 did well once I got onto a foil.

With 7.5-7.7 something just below whitecaps. Guessing around 7-9 kts. Helps to have a puff to get going but once up whitecaps not required. I've had days where there was hardly a whitecap. My big wing is around 1000cm2 and low drag.

With 8.6 I need a 6kt 'gust' to get going, but can keep flying for a while beneath that, when I'm really up to speed this 'while' becomes seemingly endless. With 7.0 I need 7kts. (Woops I believe I said already) Found out today I can do 3.6/92L/Loke1200 comfortably in 12kts (the 7.8's and 8.6's were leaving because they stood still, only some 9.2's were planing). 3.6 is my smallest sail, so everything between that also works somewhere in between haha. 86kgs and 192cm.

I have to say, I'm at a few meters below sealevel and always fairly cold, so that might change things a little ;). It is also always fairly gusty when it reaches a certain point (normal planing winds), so the 12 kts with 3.6 could also be 7-14, but I don't need the heftiest gusts to get up. In those conditions I really make it a sport to stay in the gust. (so jibe before the gust is over and then jibe in the other end of the gust, and hover/pump from gust to gust sometimes when the gust is over)

i find it really hard to make these kind of "windstrength" assesments when sailing alone, and always measure my early planing by comparing to others or looking at the environment, with 8.6 I can fly even before the leaves start rustling, with 7.0 I need the leaves rustling a little. With 3.6 I'm flying similarly early to someone planing with a 9.x, with 4.8 just before that. Other foilers mostly use 7.0 or 7.8 when I'm on 4.8. I'm reasonably convinced you don't need big sails to fly "early", as the higher the winds, the bigger the difference between what I would rig in normal windsurfing compared to foiling would be. However, in the bare minimum ofcourse a big sail is needed, but the differences become minimal between fairly big steps.