I'm 170cm and 60kg slim, i had tried on the City and Partime at the Bal boutique. Both straps are way too short to be sling across body like the messenger. So the only way is to carry over the shoulder (which may work given your style and personality)
Personally i prefer the Work, RTT, WE or Escapade, because i dun like messenger and i love BIG bags.
BTW, i think the Partime is the same length as the Work but the height is shorter.
Hope you find the perfect Bbag! Btw, what color are you thinking of getting?
Im thinking black/noir