I bought a rio small plus 205-215 soft shaft at Chattajack (31 miles, 4-6 hours) last year. I was worried about blade being too small so I started at 212cm. It has a lot of bite, grip. More than I expected. It wore me down rather quickly and I was at 205cm within 8-10 miles. I am middle of the pack 52yr old, 200+ lbs usually paddling brasca (3, 4, & 8). I might see moving to med minus for short runs, but not for long ones. I do not paddle as much as you, though. I think I read a pro, maybe Austin keifer, uses med minus. I would consider getting flexi-soft shaft (green letters), though soft (white letters) seems fine, for aging joints. You will be fine with either, only 20 cm^2 difference.
KR McGregor Rhythm, V10Sport, Swordfish S, Fenn Tarpon S, Fenn XT, Twogood Chalupski, Findeisen Stinger spec. Had: V12, Stellar SE, Huki S1-X, Burton wedge2, Fenn Tarpon