I believe the S1 was designed to be in between a the M and R in terms of aggressiveness. I found the S1 very smooth and med/mild.So the R1 is more aggressive than S1? I thought the site said it opposite...and it sounds like I have no business using any of those plates until I have perfected my technique....
I have never tried the R1. I will say that an S2 is milder than an R2. I would assume the same would be said about the SB versions.