With the barber hauler, make sure you don't have it on too tight. One of the tricks to sailing downwind fast is letting the jib breath at the top. That means a little bit of twist, lay off etc..
As far as an angle goes keeping the apparent wind at 90 degrees is a good start.
I have sailed all sorts of cats and have just bought a cat rigged mossie. I have found that some of the guys sail dead down wind. This is a boring slow way to sail in most cases and I wish that they would ban it as it does nothing for promoting mosquitos as a fast 16ft boat. Much better for other boats to see spray coming off the bows of a mossie as opposed to the skipper just sitting there.

Regards
Chris Dean