Hey Eppo,
Your quiver may be getting a bit schizoid by the sounds of it! Surely the smart thing would be to get consistent feel and safety systems across the range? K.I.S.S.

And as you've already raved about the C4s, then I'd suggest 15m, 11m, 8m to cover you easily from 11-12 knots up to 35. You've got enough experience to relaunch the 15 in marginal stuff, and the turning performance and apparent wind utilisation will keep you interested when a big delta may get a bit boring.
But from another perspective, when I notice myself putting a lot of energy into kite discussions I sometimes ask if it's a sign of authentic passion for kiting, or if it may be a way of distracting myself from from something else? These possibilities are not mutually exclusive, but for myself, I know I enjoy it most when kiting/discussion is a complement to rather than a distraction from other stuff.
Happy quiver building,
dojo