Castelli is even more confusing...as it depends on the clothing line.

For LG, I wear the elite tri suit in an M with what I consider a perfect fit. I'm 180cm, 73kg, swimmer's upper body/shoulders.

In Castelli, I usually wear M jerseys. However, I recently bought the climber's jersey and needed a L. Not only was the torso on the M too short for me, the arms, which are supposed to be form fitting for aero reasons, were soooooooooo tight. The L is still tight around the shoulders and arms, but fine for the rest of me. And very comfortable jersey btw!.