I hold them against my belt sander while spinning them with the angle grinder. Love to know a better way.
A dedicated pair of straight aviation snips. I just do straight cuts around the edges to wind up with an octagon (or whatever number of sides it ends up as) and I find that the corners have a feathering effect on the grind.
I know shops buy 7" only of the 987C and as they wear on the outside / inward, they cut them down (hand turn circular cutter) to 5" or 4.5" of 4" what ever they need. That way only one SKU to keep in stock on the shelf and not multiple different sizes. Efficient use of purchasing expense and inventory.