At 90 kg, with a need to use sails as small as 4.5 (and even 4.0), I would recommend you something in the 105-110 liter range. No bigger. The difference between +5 liters and +15 liters is huge!
A plus volume of 15 liters allows you to stand on the board with dryish feet while the sail is in the water, i.e. preparing to pull the rig. The board will sink some when the rig is upright and the board is not moving, but it should still be quite comfortable to stand on.
Any bigger board and it will be very difficult to control, and have fun on, in higher winds.
On the other hand, a 105 liter board is not really a good lightwind+bigsail (like 8.0) combo at your weight. It is not floaty enough.
Maybe a Future 111? But it may be a handful with a 4.5.