They wear and feel extremely different due to size, proportions, dial, strap attachment and overall design... The 5065 feels much more subtle, delicate and elegant, while the 5164 feels much sportier, it really looks more modern. I even wear them differen...
But I've been told that there are quite a few strap options available coming from a lady's reference which was produced in many different colors. I'll test it at the Patek Salon in a couple of weeks.