the CT 110 postie bike was first made as an ag bike for farmers. they are ultra reliable, and have a centrifugal clutch; you just back off the revs between changes and it engages. they have a 4 speed box and at full noise (when you can hear valve rattle) they will do about 80 with a full load of mail, or 90 with empty panniers.
with the rear panniers over full of mail a postie bike will do an excellent wheel stand and balance there easily (you are only meant to load 20kg of mail maximim at any one time, but i have seen up to 32).
the front is light enough to run over small dogs without seriously injuring them, and they can be ridden over any terrain, including boggy garden beds, vege patches, and new lawn.
i miss working for aussie post
there used to be a company that ran tours to cape york on ex postie bikes. They could go where 4wd's and bigger bikes couldnt because you could just about pick em up and carry them across creeks etc.