Regarding mast/strut lengths, my experiences, having an 83 cm, 90 cm , 100 cm right now:
83 is great for marginal winds, particularly in dead onshore marginal it provides an option to ride when too little wind to keep a light kite in the air without actively flying it, so not possible to drag out between sand banks to deeper water.
90 is a good compromise for everything, cheaper than a long one, and okay for most things.
But I still ventilate when frequent chop waves, which are the most normal conditions.
100 is the only one I like in normal "wind" waves - even the 90 is often too short here, where you cross and carve in close steep waves
And for riding really powered upwind, it is also better of course.
For jumping (strapped) and rotations, the shorter the better as you can tweak and turn and twist the foil way easier the shorter the strut
Strapped you can also ride faster and ventilate slightly, and recover most often, contrary to strapless, with a much shorter strut.
For waveriding in "perfect" smooth conditions, glassy and long swell period, a short strut would most likely work fine, and be quite lively.
In anything but that, which is our most frequent conditions, the longer the better IMO.
Maybe sligthtly off topic from the thread title I know, but the last posts was about differences between strut lengths.