not forgetting the internal tube has a limit to, its one of the arguements about the difference between a 30mm tube and a 25mm tube, bareing in mind some dubious peeps just stick a wider outer body on and say its a 30mm innerds..
but, if its after twighlight stuff no lights, big is better'ish..because theres bugger all about, but by day it becomes cumbersome.
andm a 80mm on speccy built mounts will probably cost a lot or, yes you wont be able to zero the scope cuz its too hi on an air gn, not forgetting the higher the scope the further the better shooting range is, like a 4x20 is low a