I left
the drywall biz in 1992, before they premade the prescored stuff.
You'll have to check code in your area, but I've seen guys either use 1/4" and score and wet it - which isn't really all that hard - just run a drywall knife down the back with a drywall square every X inches (more often for a tighter bend) get it fairly damp with a sponge and put it in place - maybe just start the screws but wait until it dries to dimple them. Then repeat with a second layer for strength (a little construction adhesive on the second sheet wouldn't hurt either!) - remembering to stagger your joints!
The one time I did it, I backed it with 1/8" cross-grain ply and then used one layer of drywall.
No matter what you use, you'll need a good taper... not easy to apply mud and sand a rounded corner like that.
Bren R.
