On my model 70 Winchester rifles, which are in .375H&H, .416-Rem mag, .458 Winchester, .458-Lott, and the .470-Capstick caliber. I only have and want 1 rear sight only. It will be set at 50 yards dead-on target. Now if I do need to shoot at an animal 100 yards away, I simply raise the elevation of the front sight accordingly.
I will know where that bullet strikes prior to the hunt at 100 yards and how much to elivate the rifle to hit the target. It is not rocket science. The rear sight is stationary and I do NOT have to flip it up, nor would I ever want to do so. I do not wish to waste time or worrying about getting the front sight flipped up in time if their should be some sort of charge by said animal.
Most of my rifles have quick detach Leupold steel mounts, using a Leupold Vari X - 3 rifle scopes on them with 1 x 4 or 2 x 7 power variable scopes. Only the .470-Capstick is strictly iron sights! It's sights are set at 50 yards, using a 500 grain Swift A Frame bullet and a 500 grain Woodleigh solid. The majority of PH's want you to have a scoped rifle verses just an iron sighted rifle......you will go to the rifle range first day prove your marksmanship for the PH.
Usually the leafs on the Express sights are filed in to suit the load of your rifle, takes a little time to do this but that's what is usually done. The 3 leaf sight is set at 50, 100 & 150 yards for the most part. I'll stay with one rear sight and simply learn where my rifle shoots at 100 and 150 yards ok.