> What number of vehicles behind you do locals consider reasonable to use a turn-out?
Out here it is generally regulated by state law. I'm ashamed to say I don't know for sure what Wyoming's limit is but probably 4-5.
ETA: those of you who say to use a lower gear or use 2nd gear, how do you do that? My class A has an automatic transmission. I have to climb (or drop) between 6500' to 6000' whenever I drive it into town to have work done. Haven't had any problems yet but I also haven't tackled the 5% grade from the summit to Laramie yet. (Driving a motorhome over the Snowy Range Scenic Byway is an experience not to be missed!)