For your 90 kg, iSonic 144 is spot on. However, if you want to be in full planing mode in 8-12 knots with only an 8.5 sail, I'm afraid it wouldn't make the cut. You'll need a much larger sail than that to start and sustain the planing (with my 65 kg, I need 10 knots wind to start planing with an 8.2 sail on any board wider than 70 cm. In that 8-12 knots wind range, I'm using a 11.0 sail). Buddies in the 85-105 kg weight range are all using a Formula + 10.5-12.5 m2 sails in such a wind range on our swiss lakes.
Another option suggested by James is to consider a Severne Glide 8.5 sail paired with a Phantom 380 (planing + non-planing mode) or even a Serenity (pure gliding mode). This is certainly a valid and versatile option if you don't want to go bigger than an 8.5 m2 sail.