I had a very good session 10 days ago in 2/3m waves. Wind was 23-25 knots with lulls at 20 and gusts at 29/30 knots. I was a little under power with my stretch quad 5'11 (was going upwind but I had to think about going upwind). I then switched to my FW Sweet potato 5'2 and was perferctly fine. I am 62 kgs and I think that 22-23 knots steady is my low end with the 4.5 with a board that works in light wind (I also uses the SP 5'2 in 40 knots when waves are not very powerful). With an hydrofoil, Stephane Goffinet is using the 4.5 in 15 knots.
jannik wrote: I'm 78 kg and was strapless without a problem.
That explains why the 4.5 is good in 40 knots for you. I also think that I can go in 40 knots with the 4.5. I am not overpowered at all in 30-35 knots but the idea was to be just fine in 35+ knots strapless hence the 3m.
As for loosing the kite on slack lines, the waves tend to float in the air. They not fall like LEIs tend to do... so pushing it to the limit in order to focus on surfing is interesting in itself. E.g., one thing that I could do with the 4.5 is to put it on the side of the wind windows, accelerate the kite and then get it to fly backwards while I am surfing down the line (in side-on conditions). There are ways to fly the Waves that are still to be explored. I think that one does not need to actively fly the kite all the time. I find it more interesting myself to only use the power of the wave for surfing and pilot the kite to follow without falling, nothing more. That was one of the characteristic that we put into the mix in our exchanges with Benoît -- the less we use the kite for surfing, the better it is.