Most of my rifles have one of 3 brands/models on them: Zeiss Conquest HD, Minox ZA5 HD or, on the lower end, one with a Bushnell Legend 3-9. None of them with objective lenses larger than 42mm. Why? I was trained in optics by a guy sent over from Austria for Swarovski in '97. He showed all of us the 'difference' that the objective makes in the amount of light that actually is transmitted by each. According to him, for the 'average' eye, there is less than 10 minutes difference in being able to discern details in low-light situations. He added one caveat: depending upon the individual's age/eye status, that amount may be more, or less, than someone else's eyes.
In short, the older your eyes get (or, if you have astigmatism or other problems in your eyes), the less the difference is.
When you compare two different types of GLASS/COATINGS in the same tube, you will see a distinct difference in the amount of light transmitted through the scope. If you doubt that, pick a Vari-x 6 and a Vari-x 1 of the same objective and ocular size and compare them in the same light conditions. The only real difference in the two is the quality of the lenses and the quality/quantity/chemical make-up and application methods used on the coatings. The differences will be obvious.