Thanks a lot for putting in a clear way what I do feel at my place.That is exactly what I have very often.
Many times winds are in the 6 to 10 knots range when with HS133 and 8.5 I can plane at the gusts with proper pumping but never could with C111.
When it is a bit higher say 8 to 12 knots then I'm planning almost all the time thanks to the amazing capacity of keeping on a plane that HS133 has, and here again I believe the extra volume makes the difference.
I believe and am eager to prove it that at such conditions I'll struggle a bit with iS105 as it will stop planning way sooner. I'll see.
One interesting point is that I can plane a bit sooner with a 38cm fin of same design and supplier - I guess - than stock 42cm. It seems to be less sticky. It also doesn't point upwind as well though.
It's really interesting to see how people make their quiver choices. It does make a lot of sense I also like less weight and nimbleness it's much funnier .I'll follow your recommendation and see how much iS105 and HS133 overlaps before deciding which iS to get although it will also depend on what will be available