As a rough rule of thumb, you’re probably right with about 1.4 times as many roof pitch degrees if you want to compensate for the room handicap of the hip roof compared to the gable roof.
That fits roughly. For example, I don’t have an attic at all, but 3.5m room height in the middle of the upper floor.
However, I also had bad building regulations, approximately 4.5m, one full floor, etc.
I could have easily bypassed the one full floor restriction with a gable roof, but my wife didn’t want that. From that came a complex floor plan with a 220m2 foundation slab.
Every building has its individualities.