I've built 135-120-110-105-90cm boards all similar construction, shape, nose rockernof 100mm. All about 46cm wide. Tried narrow tail on one and that's not advantageous.
I'm on big wing and weighing 76-80 kgs, depending on gear I'm wearing.
If I was going to choose one it would be 110-120cm.
Was on the 105 a while and it's not much difference than the 120. Been riding the 90 cm last 5 sessions and if it's light wind, it's not that good. In conditions I have sufficient power, 10 knots plus, it's really good and agile. So I have the 110 in the van if needed.
I sold my 120 and 135.
The difference in ride is agility and feel of wing is better on short board, but the difference comes from the weight in front of your front foot. So I'm doing new construction design to radically reduce nose weight on a 120cm board and have a 90 and 120 cm board. Will start building it later this summer as it's kite season now.
There's some room for innovation.
All these boards touch down the same.