Patrick Chase
I should be clear that I use diamond plates (mostly Atoma) for the vast majority of stone-flattening chores. As you say they get the job done quickly and at least as cleanly as any other option.

Unfortunately I own some stones that can't be allowed to interact with a diamond plate. For example, I stripped almost all of the diamonds off of a 10" x 4" DiaFlat (a $200 plate...) by using it to true up a Sigma Select II #240. I expect that I'd see similar results with coarse SiC-based stones like a Crystolon or my Sigma #120.

I use a well-worm Atoma #140 plate to flatten stones down to #320 or so, but below that I switch to loose SiC grit. It's almost as fast as a diamond plate once you have the hang of it (and figure out some tricks like using sacrificial plastic laminating sheets to "hold" the grit), though it makes a god-awful mess.