GC has posted some general scaling values for the current implementation of stormlash totem.
"Fundamentally, there’s a base Stormlash damage, which is currently (but may be too strong) 30% of SP or 20% of AP. Then, various attacks deal a percentage of that base damage. Auto attacks deal 40% of base for main-hands, and 20% for off-hands, and are
normalized to a 2.6 weapon speed. Spells and abilities generally deal 100%, and are normalized to a 1.5 sec cast time. It generally only procs from direct non-periodic damage, but there are exceptions for Mind Flay, Malefic Grasp, and in the next build Drain
Soul. Finally, we do customize these formulae for certain spells which we want to tune to be stronger or weaker, to make up for significant deficiencies or proficiencies."