A DA will cover a lot of area. Sit down if you can by raising or lowering truck. I use a DA and an old fashioned square face "orbit" sander for the major removal. I use a big fan to blow right where I'm sanding. Cools me, the sander and keeps the dust away from mask. Mask is a must.

HEAR YE, HEAR YE:
I don't know how thick or rough you have it BUT most body men would probably NOT use a DA. I do, but it is to get it to where a real body man can finish. Mostly of my work is just covering patch welds. So I don't want to encourage or discourage anyone. I can not finish a panel good enough to paint. When I think it is as smooth as glass, then paint, it looks like cellulite with pits. A DA is better suited for paint removal down to bare metal. I use it for that mostly, as well as a wire wheel.

The proper method for filler is block sanding. I realize you know that and are asking about "rough cut". Pro's will rough cut with graters and block sanding with 80 grit. I would not sand a whole panel or a whole truck if you paid me. It takes FOREVER!!!! and you will never get it smooth and "straight" for primer/paint.
Anyway that's what I think.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn