Two days ago, I finished that. It's not sanded or painted yet, but it's not fiberglass hanging out, either. After cleaning out the ants, I replaced the insulation, and then it was time to start.
The first sheet took way too long. I'd measured the height of the sheet at the front of the frame on top of the opening, but nothing in this opening is even close to square. So I ended up cutting off another half inch or so, a little bit at a time. Ugh. But finally it was in place.
This is the first time I've used full sheets of this mold-resistant cementitious wallboard. It's heavy, way heavier than conventional drywall. Still much lighter than a wall made of bricks, of course. In comparison with the rest of the building, this wall feels distinctly flimsy.
For the second sheet, I measured the height of the first sheet, determined not to make the same mistake. So naturally, this sheet was an inch too short on the left side. Oy. It didn't even come up to the 2x4 frame-in. The answer: lots of spackle, oh well.
The wall as she looks today - I spackled in around all the edges, and the result is pretty darned nice. My next trick is to sand all the spackle and paint it, along with the frame of the old garage door.
I'm using "Ultra White" latex paint for these walls. I like white, a lot - and I have to say, I'm really liking how it looks in this basement area.