[Runner]

Seems like several questions here:

First, which one is most useful? To me, the angle grinder is hands down more useful. I have a Craftsman 4 inch that's been great, and a Makita 9 inch that is also a real animal.

One thing that the big 9 inch is really great for is wire brushing. With a wire brush wheel, that thing will remove all paint, rust and anything else (including skin) quickly.

Which is best for the job at hand? Between those two, I'd probably pick the bench grinder for the job at hand.

However, you also mentioned a metal file, and for me, if I have a small amount of metal to remove, like a couple of millimeters over a small area like you are talking about, I'm just about as likely to reach for the metal file.

A Dremmel tool with a grinder wheel or small sanding drum also works great for that kind of stuff, as well as a die grinder with a metal cutting burr if you don't need to be too precise.

Best of luck on the project.