What size twin tip were you riding?
Have you ridden any of the other light wind kites and how does the 16m Nitro compare?
I ride a LF Influence 140 with boots.
Unfortunately I haven´t tried any other lightwind kites, but we have many zephyrs and Flysurfer monsters ala 20m2 something on our spot. It has considerably more power than my 14m slingshot rpm anyway, and I can get going about 3-4 knots earlier, I believe.
I rode all day today with the nitro, the wind speed was between 10-15 knots. In the morning it was 10-12 then it increased to 12-15 knots.
I can anyway say that no zephyr could ride when I couldn´t.
The flysurfer monsters could obviously get started a couple of knots earlier, but then they rode monsters doors as well.
When the wind was blowing 12-15 knots, I had full power, if the wind had increased, I´d been rigging my 14m.
Sorry I couldn´t answer all your questions.