We run at 4.7 metres but our loads are toilet roll (v busy this week, can’t think why?) otherwise the more the frontal area, the more fuel you use pushing air out of the way. Plenty seem to manage at 4.2-5 and when tipping on bays the height is a major and sometimes expensive problem. Usually have to wait for decker bays which are not so plentiful. If you do need height try a low ride unit - it will save diesel but is a bit specialist to move on.