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if you are not interested in foils, no need to read the below. Peace.

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Hi Cezary,
Lucky you if you can afford a Speed3 in Deluxe version! From experience, the Deluxe fabric being lighter, it makes a significant difference of handling comfort in 5 to 10 knots of wind: the kite has less chance to drop into the water in lulls + it flies easily toward the top of the window making it easier to generate power and keep the flying speed up... Not sure of the exact % but I think the Deluxe kite is about 20-30% lighter than the standard version of the kite, and in light winds this is a massive benefit that you can feel straight away.
Not sure what is your background and what was your biggest kite until now, but kiting in 10 knots of wind can be awesome fun if you have the relevant kite to generate enough power... In regards to size, to my humble opinion, based on the Speed2 experience, it would be a shame for your weight to go for the 12m: for water use and 80kg, that's not a super lightwind kite! (though for land kiting or snowkiting maybe if that's what you are into!?)...
So, I would strongly recommend the 15m or maybe even the 19m. Flysurfer is not claiming they have improved the low en of the Speed3 vs. Speed2, but they are claiming they improved the turning and stability (and I am already convinced it is true, based on the Psycho4 technology which makes it turn faster while depowered)... so the Speed3 15 should be really sweet for 60-80kg riders I think, and the 19m for heavier ones.
I guess it also depends on what other kites you have. For me, about 65kg with one single board (130x39 TT): Speed2 15 (sweet spot 10-15knots), Psycho4 10m (sweet spot 15-25 knots) and Psycho3 6 (sweet spot 25-40 knots), it is really great!
In case you still want to go for a 12m, I would not see much point going for the Deluxe, because it won't get you going in less than 10 knots, and in that wind, it does not matter as much to have the light fabric.
bye
Jacques