Much of what you say is correct.
I can assure you though I have sailed in 35 knots with gusts to and over 40 knots with a really flattened off 4.5/4.4. (4.5 Rock/4.4 Combat)
My weight of 105 kilos is obviously a consideration.On day in question there were sailors out with sub 4`s and some on 3.3`s but I have found with such sails my range is (at 105 kilo) non-existent.
Your points re waterstate are correct.My PB (V max 10 second;dont think 2 second is reliable or valid) is 42.6 mph (just under 40 knots) set on mirror flat water in 30 knots (ish) with 5.7,(On Sotavento speedcourse;feet from watersedge)
Decided last year that anything under 4.5 weather for me was unenjoyable ;sold 3.7 and rarely use 4.
In my case I dont think my upper limit is much different (sub 4.5 too twitchy) and look on gusting to 40 knots (35 knots steady ?) as just worth rigging.Over that stay in car/go home.
Its the gusts and lulls that get you anyhow;steady (even strong) are manageable.
Its true we all think we sail in stronger winds than we actually do but 35 knots + is common at Leucate and there are days when I dont even rig and some sailors (smaller than me) are out sailing. Reaslistic upper limit for windsurfing (IMO) is 45 knots. I look at 40 knots as mine.
Take a look at Port Leucate wind record (Windfinder/Windguru) after a Tromantane has blown through.
Last Saturday was a "typical" day. Trouble is there are just patches of flat water where sailing seems much easier; and Tromantane is a notoriously gusty wind .
Kiters do deserve recognition for progress.