Dunno why you'd think I would be along with useful info - in my day you started off with a conservative guess - added 1 more bag of coffee (40-50kg) on each subsequent trip until you gave your self a fright and the next time lifted one less bag of coffee....worked good.
I do remember there was a section in the Talair Islander ops manual with MTOWs for a bunch of steep strips - if memory serves some had MTOWs < BEW - which indicated immediately that further reading was merely blowing sunshine up the ar$e of whomever wasted their time writing said drivel.
Beyond such high brow considerations we just figured steep was good...REALLY steep was Gooder.