Good question - my thoughts (without ever having ridden one above 7.5):
Rider weight means everything, so if you are over average weight 75-80 kg, bigger sizes will make a lot of sense.
Also, Hybrid simply feels a lot better turning than Peaks, I dont like the Peak 8 m2 - yes it can be a session saver as it can give you 1 knot better lowend, but on cost of bad drift and lousy turning (IMO and experience).
So I use my 8 m2 (too) often because of too little wind for the "perfect" 6 m2 and smaller.
The 7.5 Hybrid has a bit less power than its size, but it is AWESOME for playing around in the waves, feels like a much smaller kite.
Meaning, a 9.5 might have the same advantages, and then an 11.5 could have the same for heavier riders.
Anyways - the option to be able to relaunch these kites, are quite attractive IMO, as the only kite I have dumped and had to swim, has been the 8 m2, as used in these 8-9 knots of wind where dropping winds close to "mirrorwatersurface" CAN happen...
The lack of peak power would make very expensive twinskin foilkites even better, yes, but they will turn like dogs, compared.
So not that easy to predict
Peter