Man I think arms can be a tough one for sure if they are lagging. Also being the one besides chest most people want. As far as short and long head on your bi's I would take the longer ones anyday. Just build them up and get a big peak on them.
As far as bulding them up, I don't care what people say, I think some people need more reps. Just take my boy Lee Priest. He trains the crap out of his arms and they are massive. Once I jumped on that bandwagon I have gained well in the arm dept. I would bump up the sets and go to a 4x8 routine if it was me. I would also train arms on their own day. Just my 2cents. if it's worth anything.