Hi,
I've just finished grinding a 33"f3.55 mirror (all without the use of any machinery). Grit progression I used: (All Sic) #36,(hogging),#60,#120,#220,#400,#8 00 (22"glass tile tool).Now ready to polish using Cerium Oxide.
For small mirrors (up to 8-10") I have used #80,#220,#400#800 grits only.
For Medium size (12-16") #60,#120,#220,#400,#800 is OK.
No need to obsess overly on how close/wide the grades are.
Stephen.