Riding with long cranks 150 and longer on a 36" are ok but it meaning you are fighting the wheel as you would a muni. To get the best out of a 36" is to go with the flow. It is the boss!
It is a totally different machine with shorter cranks. There is no messing around idling - they just go and are super smooth and flowing. The shorter cranks give you considerably greater speed when you get in to the grove with them. So if you are doing 10mph on 150mm, it will be 15mph with 100mm.
Climbing with the long cranks you are doing it stroke by stroke. The shorter cranks you need to spin to keep the wheel moving smoothly. 125mm is the sweet spot for many beginner/intermediate riders as it allows you to keep the spin up and lots of control. The other sweet spot is 110mm for many riders. It gives quite a bit of control while still giving amazing speed. I have had 89mm on mine for so long I can not go backwards.