Since your objective is to remove a lot of metal quickly when restoring knives, you might consider using various grits of Silicon Carbide wet/dry sandpaper. Get a piece of glass or granite to use as a backer for the paper.

Since SiC is harder than most other abrasives except Cubic Boron Nitride and diamond, it works quickly. It also has a particle shape that is great for metal removal.

I have the 400 grit Superstone. I have only used it when I had to remove a bad chip in the toe of a vintage razor. For razors, normally 1000 grit is as course as needed.