Hi guys, I'm relatively new to fountain pens and I'm in a process of buying a Pilot Custom 823, but I'm having a very hard time deciding what nib size I should choose. I find myself at ease with the line width of pens like the Pilot Metropolitan (MR2) equipped with an M nib or other non-fountain pens such as the Pilot Hi-Techpoint Roller V5 or the Pilot Vball BG 05. Knowing that, what would you suggest me to choose: the F nib or the M nib? Thanks.