...t the "twilight rating" is different. Maybe my brain is broke. Experience with both in low light would be great. Is the 6x42 going to have as nice of a sight picture as the 8x56? ...
Sorry, I should have answered your questions. I use both the 8x and 6x for hunting.
Regarding the "twilight rating". It's a formula for low light viewing. I believe it's the square root of magnification multiplied by the diameter of the objective lens. So the higher the power, and the larger the objective, the greater the higher the twilight rating. It doesn't factor in glass/coating qualities, number of lenses, eye relief, etc. An 8x56 will always have a higher twilight rating than a 6x42, even with crappy glass and coatings in the 8x, vs "the best" of both in the 6x. It's just a formula.
I use both the 6x42 and the 8x56. The 8x56 is brighter in low light and will allow better vision in low light. Every time I look through the 8x56 I'm impressed with it in low light. I really like to look through it. That said, I rarely use it. When I have a short evening sit over an ag field/wood line edge for a 300 and in shot it's a perfect scope. Because it doesn't have an elevation dial or windage holds I don't like to use it past 300. Because of the power and FOV, I don't like to use it in woods. I use the various 6x's (depending on model/reticle) in both those situations, as well as the ones where I'll use the 8x.
I like the 8x S&B. If it was available with an elevation dial and a reticle with windage holds I'd use it a lot more...but I doubt I'd use it as much as I use a 6x because of the 8x's weight, size, and use in all ranges/conditions.
The 6x PMII mentioned is my favorite scope for "everything, everywhere". I like simple things.