I did watch me and my friends' touch typing behavior, and most of us use left index finger for RFCVGT(B), and right index finger for YUHJ(B)NM. the character in parenthesis means it overlaps between right and left area
That's what I do. I'm clearly wrong about the fingering charts though (I learned from an ancient DOS program, so I can't check that one). I have a picture of a symmetrical one in my head; C is the equivalent of M, so it seems like they should use the same finger.