DMT is at the bottom of my list for quality. Moonstones are very good. Swix are better. My quality basis is, ease of cleaning, life span and how efficient a job it does on an edge
I just got one from Holmekol. It is 120 grit, their coursest and awesome. You can buy replacement diamond strips for it that are afixed with an adhesive backing. Absolutly the thickest diamond surface I have seen in a stone. Darn near as good as a file.http://www.holmenkol.us/
If you can find your local area Holmenkol Race Service Rep. He might be able to get you a passcode to get a big discount off of a website purchase. Especially if you are a card carrying USSA Racer, or maybe even just a nice ski enthusist. They have great wax too. Competitivley priced. IMO,There are only really three wax maufacturers that have fast dinosaur wax these days. The red, the yellow and the blue companies. Swix, Toko, & Holmenkol.
IMO, you only need a 100/120 and then a 400and then an Arkansas stone.