My personal opinion is that scopes have an advantage in the accuracy department and open sights are much faster. I don't beleive a scope is faster at all. That is just my opinion though.
It really depends on what you want to do with the gun and how far you want to shoot it. There is no question at longer ranges and higher magnifications a scope is much more precise. I mean you can't hit what you can't see. I would never expect to shoot 1 or 2 inch groups at 100 yards with open sights. Heck the sights will probably cover the whole target. How do you expect to hit a 1 inch square consistantly? Same with a low power scope. I'm sure my slug gun would shoot better groups if it had a 10 power or higher scope on it. Wouldn't be very practicle though for what I want to do with it.
However for hunting at the distances you are talking about either should work well. If you are comfortable with open sights and use them well I would go that route with out hesitation. They are lighter, sleaker, less prone to breakage or malfunction and easier to use. It's just a much simpler design. The trade off is you don't have the amount of precision you have with a scope. But then you don't really need it for deer sized game at 75 yards.
Now if you wanted to shoot a high powered rifle at 200 plus yards or were shooting at smaller animals or target shooting I would suggest a quality scope for sure. I personally like scopes. However I do more than hunt with my guns, I like to see just well I can shoot with them for my own satisfaction. And admittedly I am not that great of a shot off hand or with open sights. But I do know the limitations of a scope as well and fully except them.
I try not to worry about the light gathering side of a scope. I mean I don't want one that is dark and hard to see thru, but pretty much every scope on the market now is plenty bright. I do however like a scope that has good clarity and resolution, and this is usually where the increase in brightness comes from. It helps if you use it in shady areas where the light changes a lot. I don't feel light gathering is a huge advantage in most situations though. I bet if you had to rely on the scope to gather light so you could see the target you would not be in a legal shooting time any way. Unless like I said above, you were in an area where there was lots of cover and the light was not that good to begin with. Although in those situations it is harder to find your target in the scope and I think you would be better off with open sights since they are quicker and you never lose sight of your target.
Another option would be a red dot type sight with no magnification, or a 1 power scope.
I personally like fiber optic open sights for my turkey gun. They are quick, easy to see and plenty accurate.
I don't think I helped you one bit did I
After reading all your posts on this subject here is my personal advice. If you were my friend and we were in the store together this is what I would tell you to do. Get a tracker II 20 guage slug gun with open sights. Get a good recoil pad and maybe put a little weight in the stock. Then go out and kill some deer!
That or a 870 combo package with the rifled barrel and open sights. That would give you an easier follow up shot when doing drives. However it would probably cost twice as much as the tracker, of course you would be getting two guns in one. Keep in mind you can get different barrels for the Trakcker II as well.
Take the money you saved on the scope and rings and spend it on different ammunition so you can see what you and the gun likes.
Good luck,
Paul