giant bikes

I currently own Giant TCR advanced Pro and Reacto 400. TCR feels light, nimble and its great to ride, however, on heavy winds TCR tends to have a "Snake effect". Im looking for an upgrade and have shortlisted Pinarello F5 and Giant Propel Advanced 1, F5 comes with Mechanical Ultegra groupset...

I am planning to Giant TCR Advanced Pro Team Road Bike. My height is 178cm (5'8") and inseem is 84cm (33"). Should i buy M size (47) or ML size (50)? My friend say M might look small for me and considering my inseem ML might suite me. Please help.