Gun size question....

Hi guys, Newbie to the board, i had my first encounter with spearfishing this summer and its got me completely hooked :). Initially i just had fun with an old mares arbasten 75 and practiced for a month or two, but my plan is to really get at it next summer. So now im stuck at the decision of what gun to purchase.

Im swinging between an omer hf, omer kanaloa, cressi comanche pacific and the cressi geronimo elite. Ill still see which one it is out of the lot depending on what i can order here. But what is bothering me is what size i should go for.

Im fishing in Montenegro, its a small country just south of Croatia, and i would target: Atlantic bonito, Leerfish, common dentex, gilt-headed bream, european seabass, and Grouper.

Sorry if the names are wrong, im translating by searching for the latin name, then to English.

The guns i did pick all have take two circular bands. And i planed to add two 16 or 14 mm bands. Then when going out into the open hook both bands, and only hook one for fish in holes like grouper and similar. Is this reasonable, will i get too much tangle and what not with one band swinging off freely?

So going from 90 - 110 , what do you guys think?

Thanks in advance.