My runner girls "chatter" all the time, which is like soft short quacky noises in quick succession, but they really quack properly when they get scared or excited. The boys just aren't as vocal generally as well as having the sound of a sore throat!
From about 3 or 4 weeks, my boys were taller and longer legged than my girls, with one boy having grown a good couple of inches taller than the girls already. They also just had a "boy" look about the face, while the girls were bossy, more confident but dainty and pretty looking. You kind of just get to know by watching them grow.
Having said that, still waiting for curly feathers to confirm what I think I know!