RE: F160 and R19
I wouldn't know about the Drake R19 but the Deboichet R19 (in the S-- +8 configuration) works well on the F160 in low winds, though I'd believe it overpowers pretty soon with a 73kg rider. In less than 15 knots you'd probably be ok though.
Do you feel the current R13 stalling in low winds? A softer fin with more rake (like a R13S+8) would probably be a lot better too.