Finn Aagaard did an experiment comparing the speed of getting on target and shooting with a scope versus a ghost ring. Surprisingly the scope won out very slightly. The scope was a 2 1/2 or 4X and was used with both eyes open. It was not a scout scope. He prefered a low power scope on his big game rifle.
I think it is a matter of practice. I can get on target very fast with a 4X scope. I use both eyes which I think makes a very big difference. A ghost ring is the only thing I think comes close in speed--you just point the front at the target. A scope is similar in that you only have one plane to focus but traditional open sights have two planes to line up (including express sights) and are much slower in my experience.
I think it is a matter of practice. I can get on target very fast with a 4X scope. I use both eyes which I think makes a very big difference. A ghost ring is the only thing I think comes close in speed--you just point the front at the target. A scope is similar in that you only have one plane to focus but traditional open sights have two planes to line up (including express sights) and are much slower in my experience.