I'm 5'11'', around 75kg (165 pounds), thin...
I'm 5'11'', around 75kg (165 pounds), thin build. Should I go for the M or the L?
Go medium if you want a more classic fit, choose large if you'd like a baggier fit. Personally, I would go large if I were you but I like a baggier fit.
I would run the Large for sure, especially if you are going to ride in this jacket.