I was riding recently smaller bike, ST 52cm, TT 54cm (my old bike ST 58, TT 57).
Although frame is too small for me, I was riding very comfortably, I think that's because TT is shorter.

However, I hit occasionally shoe against the front tyre so when measuring frame I would also pay attention to bottom-bracket centre - front-wheel centre. In smaller bike it is 2,5cm shorter (both bikes crank 170mm).