I'm from Brazil, my friend is from Argentina and he is having the same issue, another one on Japan is downloading with good speed, but the Australian isn't.
If I use the download accelerator, or anything else to speed up the connection, the download keep the same speed with more connections, so, I believe something is restricting the speed, maybe a script from arcade, to maintain the site and the server throttling always low.
My main site is located on Texas, I have a slot there, and my route from there is very fast, like the route of my another sites located on Massachusetts.
But I stop here, because I'm not an expert in this issue and I can't help much more than this descriptions and tests (made by my friends).
We can host the files on mirror servers too? like dropbox (posted on topics, for example).