I'd say just as fast. Same thing for both the peep and scope, if the gun fits you and you practice, the sight picture is acquired instantaneously.
The (perceived) difference is on followup shots. I say perceived because it "feels" quicker to reacquire a target coming out of recoil with the iron sight. In fact, there is no difference, similar to guys thinking they shake more on a higher power, when they are in fact shaking the same but the higher magnification, duh, magnifies it.
We will have to agree to disagree. Looking through a tiny pin hole more than likely with one eye closed you loose a lot of peripheral vision. Open sights are faster acquisition than peep sights and better to swung on moving targets.