So, downwind - my answer for 5 is what you're looking for - the reduced atmospheric pressure as you increase altitude reduces the exhaust backpressure and improves the cylinder filling.
Not being a smartass; I note you're locale is australia, assuming you're studying here, a chunk of this is covered in the aviation theory centre PPL/CPL books, the first book I think, I'd give you a reference, but I can find every volume but the one I need, sorry!