Hi, I'm Nicolas from South of France (sorry for my english which is not very good).
I like very much the pneumatic spearguns, and specially the Mares sten. I have 2 sten 13 (84cm/100cm) and 1 hybride sten 13/seac hunter (120). But before, i had bands guns, mares sten 11, seac asso, mares Spark and i have tested other pneumatic models like cyrano, airbalete, or LG Manilu. I prefer the 13mm barrel with an 7 mm spear (for fishes from 0.5kg to 10 kg).
I agree with all what u said about the comparison between 11m and 13mm barrel. I would ad that 11mm barrel guns are lighter than the 13mm barrel. Even if with a dry kit the difference is less important, it really matters for the small guns which are very heavy to my point of view.
Moreover, wether is a 11 mm or 13mm barrel, magnetic line releaser (i'm not sure of the), is paramount to avoid hard trigger. I bought pelengas line releaser for all my sten for this reason.
In my situation, i think that the sten 13 mm 84cm with a 7mm spear (devoto or sigalub), a dry kit (salvimar in my case), a pelengas line releaser and pelengas slider, is most multipurposed gun i have. For this small gun, the neoprene sheath is not an option because of the original awful balance!
I confirm that you can reload the salvimar kit under water, even if, it's better when you reload the spear out of it.
When it comes to dry kit, can tell me more about the tomba Kit? We don't found it in France. I've already had/tested STC, LGsub or salvimar (and others like pelengas or UBL), but i don't know the tomba kit.
have a good day!