I use diamond plates for hand-sharpening (with window cleaner as lubricant). Specifically, I use DMT Dia-Sharp continuous diamond plates and I currently own four: coarse (320 grit), fine (600 grit), extra fine (1200 grit) and extra extra fine (8000 grit). I am truly happy with only the coarse and fine.
I don’t know if it’s the wheel on my sharpening guide or bad manufacturing luck, but both the extra fine and extra extra fine plates have developed a stripe down the center where the grit has worn almost completely off. This happened almost immediately with the extra extra fine and took about a month of heavy use with the extra fine. I try to change up which parts of the plate I use, but for thick plane irons, I have no choice but to run right down the center and the difference in grit leaves a dull hump in the center of the irons.
So I am trying something new. Rather than purchase replacements (new territory for me, I know), I have decided that from now on, my plane irons are only getting sharpened to 600 grit (i.e., on the fine plate). After re-watching Paul Sellers’ Sharpening to 250 Grit video a couple times over the last few days, I think it will be okay (I sharpen pretty often as is). I’ll still do my chisels and router plane irons to 1200 grit on the extra fine plate (since I can run them up and down the remaining grit on the sides).
I don’t really even use the 8000 grit plate anymore. Given how proactive I am with re-sharpening, I haven’t found the extra effort makes much of a difference on edge retention. And I think I remember hearing somewhere that the edge dulls to a lower grit pretty quickly anyway, so what’s the point?
We’ll see how it goes. If nothing else, it will cut the weight of my tool chest by a diamond plate’s worth of ounces.