I just completed stripping down the 2 sides and front of the bed for my 54 3100. This was a bed I located at a salvage yard and had shipped to me. My project truck had a home made flat bed and I wanted to put an original bed back on it. The bed parts were covered with about 50% original paint and the rest was heavy surface rust. I discovered a two step approach worked best. I used a random orbital sander with coarse paper. I hooked it up to my shop vac and there was virtually no dust. This did a great job removing the paint down to the bare metal quickly but worked very slowly trying to remove rust. I did change sanding disc frequently. After removing the paint I switched to an angle grinder with a cup knotted wire brush installed. This did a great job removing the surface rust down to the bare metal but struggled on painted areas. I had a total of about 3 hours invested in each of the 3 pieces. I thought this was pretty quick for stripping paint and rust. As stated above, there are multiple approaches, so experiment with different methods before investing a lot of time on any one. The two step approach worked great for me for a combination of paint and rust removal.
I've used your method before and basically agree with your findings/ approach for DIY'ers.
Just make sure after all the wire wheel/cup work you go back over the piece with 80g sand paper.
The metal needs to be roughed up and given some 'tooth'(teeth?) for your primer (or filler if you go that route first) to adhere to.
