I'm 6'2", with medium length arms and legs (I think!). 56cm is too small for me.
One of my earlier bikes was a 56cm Felt frame, which required both seatpost and handlebar extensions. Rode this for many thousands of kilometers with no (back/muscle/arm/leg) problems. When my next bike had a bigger frame, I realised how the 56cm didn't really fit me at all.