8x30's only have an exit pupil of 3.75mm - the human eye can only digest 7mm of exit pupil (light that reaches the eye)
a 7x50 bino has an exit pupil of over 7 - you would notice a big difference between the 7x50 military marines, and the 8x30's you have.
they larger the exit pupil, the brighter the image - divide the objective size by the power = exit pupil.
BUT glass quality is just as important in some cases, and the military marine is not steiner's best glass/coatings.
i hope this helps. Steiner DOES make some good stuff.
J