Re: scope power
The real limit for the amount of brightness you see is the human eye. The rule of thumb is the objective diameter should be 5X the power to get full brightness. The iris of the human eye is normally limited to about 5 to 7mm. Scopes (and binoculars) with more than that 5x relationship between the power and the objective diameter are a waste as the eye limits the brightness.
While there are 7/8 inch scope tubes as well as one inch, and 30mm, Leopold makes a tactical 34mm tubed scope and my Millet for our 50BMG is 35mm with special rings. The manufacturers of scopes have to do ray traces through a potential scope design to determine the tube diameter that will work. It is a function of both the magnification, the length of the optical system, and the objective diameter.
Another limitation that the objective diameter places on the user was recently brought home to me (again) when I used a gun with a small objective diameter. That limitation was the diameter of the field of view. That is, with this particular scope your eye had to be perfectly lined up or you suffered a blackout. The alignment of eye to the scope was very critical and an increase in the diameter of the objective would have made that effect less.