Off hand, my best guess would be that under classic low light conditions, a good, or even the highest quality, 8X56 rifle scopes won't do anything for you that a good 40mm variable won't do. That's because at worst, you are dealing with a situation that can handled by a good scope with a 5mm exit pupil. In fact, I've seen lots of "low light" and "last of the legal shooting time" conditions where a 40mm scope set at 10X will work. If that's the case, you'll be able to see further than an 8X56 scope can. On the other hand, a decent 8X56 scope can see quite well under true night time conditions where a 7mm exti pupil is required.
Low light conditions mean different things to different people. That's because some of us have lost some of our night vision. While the usual rule is a 5mm exit pupil, some can't even use that. When it gets dark enough, nothing works for such people. Only people with eyes still able to use a scope with a 7mm exit pupil can use such scopes, or scopes set to produce such exit pupils.
I might add that I've used binoculars and rifles scopes under unusually bright night time conditions where they worked with as little as a 4mm exit pupil.
I'm not of the opinion that scopes with 50-56mm objectives are useful to me. But I have no doubt that they can useful to some who hunt in bad light. Besides being useful in full darkness, they allow one to use more magnification and still have enough exit pupil to be useful. Such scopes will allow one to see further because they use more magnification.
Then we also have the type of reticle used under low light conditions. I've found that one really doesn't need to see the target all that well under many low light conditions. But, unless the target is pretty close to the shooter, say 50 yds. or less, one must be able to see the reticle. Especially if the target is on the order of 150-300 yds. out. E
