My observations:
double skin racing kites have a huge amount of power on hand for light wind foiling ... however, people are using huge kites to generate that power. I see the race foilers able to go 25 knots plus in 5 -6 knots of wind using 21 m high aspect race kites. They are, of course, slow turning, but I never see them gybing in very light wind, only tacking where that is less of an issue. The kites will sit on the water ready to relaunch in a gust of wind - I'm thinking more than the 5 - 6 knots, as long as there isn't a tangle in the bridle, which can happen quite easily in very light winds. As far as can tell, swimming in with a large double skin foil kite is no joke.
I suspect single skins - like my Peak4s - aren't efficient in very low winds because they lack structure provide by the internal air pressure of double skins. So, there is a law of diminishing returns with bigger single skins. Peaks excel at a very specific type of foiling: playing around in swell & waves, particularly going downwind. They're not very good at other stuff. Swimming in with a water-logged Peak isn't much fun. Much easier if you have your board (preferably not too small) to put in on after rolling up. I now wear a proper PDF when foiling with my Peaks, because should you become separated from your board, swimming in carrying a Peak is really challenging.