Don't take this as gospel, but I believe it to be true. When I was researching binocs and scopes some years ago, I read that by dividing the scope magnification power (let's say 6 power) into the objective bell size (let's say 40mm), you'll get a ratio, which in this case is 6.67. If you are a young guy, as I once was, the most you can benefit from would be a 5. As you age, you won't be able to utilize or benefit from as much as 5. So in a scope with a 40mm bell, the max power you should use at twilight would be 8 power. Of course, you'll need to factor in the quality of the scope. Better scope means more available light for you.
Taking all of that into account, just buy the best scope you can afford and keep the power below 8 (or less) at twilight to pass as much light as you can. Whether or not your aging eyes will benefit from maximum passed light, I can't say.
Due to a brain tumor (since resolved), I spent about a year wearing an eye patch. Looked pretty cool and drove some women wild (and...unfortunately...some guys), but the world is dimmer with half the light coming in. And that ain't theory...that's a fact.