People think iron sights are faster than scopes because they can see the sights just by looking down the barrel, but I think it takes longer to line up the front and rear and then actually get a bead on the target, than it does to get the reticle of a scope on target. my AR15 has a fixed 4X scope and I can get on a lightswitch cover at 5 feet away within 1 second of shouldering the rifle.

One of the advantages of a scope is the light gathering ability at pre sunrise and after sunset legal shooting times. Magnification is another advantage of a scope. As far as speed, you cannot beat the speed of a holographic sight. For iron sights, it is hard to beat the speed of a hooded front sight like the Marlin lever action rifles.