I like the DMT course; it removes metal fairly quickly, and doesn't take nearly as long to clean up the deep scratches as from the XX course.
If your doing ODC, have you considered a belt grinder?
The difference between try and triumph is a little "umph"! NO EXCUSES!!!!!!!
I have a Shapton Pro 220, and it works pretty decent.
However, if I were to need another, I would want to try the Sigma Power Select II 240, as I've heard great things about the speed of this series, and price isn't bad at $55 from Lee Valley.
I really dislike using diamond plate on knives, feels horrible, for down and dirty work I use naniwa 150. Plate strictly for flattening. Gonna try chosera 400 per kfeds recommendation.
chosera 400 is not the same kind of stone as the gesshin 220. In fact I'd say the chosera 400 is more akin to the gesshin 600. I own the gesshin 220 got it back around January and I bought it for the exact task you are suggesting because have worn down enough 400 and higher stones and rubbed the diamonds off enough plates so i wanted to see if it would be a cheaper option I was comfortable using. Being that it is 220 its a bit of a bumpy ride and the steel makes a loud noise as you use the stone. I think if you have used a low grit stone before they are all pretty similar in this regard but the gesshin doesn't leave an overly deep scratch pattern which I always hated about the extra course dmt or atoma. I have a few higher grit diamond plates but I like them better for lapping and I think the 220 stone or any stone feels better then any plate I have tried and again price is always a consideration. anyway my final thoughts the gesshin does dish but its not so fast I have had to stop thinning and reflatten the stone but I guess it depends how much thinning you are trying to accomplish and the steel you are thinning. I too had considered a belt grinder but obviously I'm interested in something variable speed and then cost is a problem again plus I like and am used to free hand... belt grinder seems like a whole new skill/position to learn or get comfortable using. then there would be the whole issue of explaining why I need this space to setup my belt grinder
anyway goodluck sir im interested in hearing what you decide and if whatever you decide on meets your needs.
The only real success I've had in thinning odc knives is a belt grinder. Have to go to my buddies shop but its definitely worth it. So much faster on the stones or diamonds I just can't stay focused long enough to do it