I've been grinding metals and glass for more than half my life and prefer the loose abrasives (aloxite) with water than the diamond abrasives, but others prefer the diamond products check these sites (I have no commercial contact with any of these)
http://www.engis.com/
The loose Aloxite powder grade I use is graded at 302, 302 1/2 and 303 for finishing, just got back to work from a customer and leaving in 10 mins, will post more tomorrow.
It all really depends on how much material you want to remove- you need to work down from rough to finishing grades on either choice.
The oil based diamond products are a pain to clean off and tend to "clog", although others may say that the diamond products remove more material, I find that for total control of surface profile the Aloxite and water is better.
Post more tomorrow.
I love deadlines- I like the whooshing sound they make as they fly by.