I have only used the DMT continuous plates. I have lapped with the XX and the C and always under running water in the kitchen sink when at home or when at work in the sink at my tattoo station. Full disclosure, I use the DMT D8C at work and the Shapton GDLP with interuppted surface at home but always under running water. In the case of the DMT continuous plates the running water eliminates stiction issues for me.

I bought the XX DMT8" 120 grit IIRC because ChrisL and Utopian suggested it for barber hones. I have since quit lapping barber hones and just clean them throughly. Something I am experimenting with. What I have found the XX great for is preliminary lapping. I'll take the pencil grid down 90% of the way and then get the last 10% with the GDLP. This expedites the lapping process and conserves the diamond surface on the more expensive Shapton plate.

At one time I used my D8F 1200 to lap. I was noticing a gray residue on my Norton 4000 and wondered what it was. Fortunately for me my 1200 was new and Sham posted that he had ruined a 1200 lapping hones. So I realized the residue was the surface wear on my plate and quit using it for lapping in time to save it. Subsequently Dia Sharp, the makers o fhe DMT line, posted in their FAQ that waterstones should not be lapped with anything finer than a DMTC and that under running water.

They recommend the X or XX for lapping waterstones. I also have a credit card sized DMT 325 that I use for creating slurry on stones for which I don't have a matching slurry stone. This is very effective and convenient and they are relatively cheap.