Have you thought about any other "Mac" names? McKinley... Macauley... Maclean... ummm.... I'm sure there's more - have a look through the phone book maybe?
I think it's not so nice to have a name that is mistaken for the wrong gender, especially for boys. I have an uncle with a "girls" name, and he gets mail addressed to Mrs. So-and-So all the time. Must have been brutal in highschool.
But my perspective on MacKenzie is also North American, and it could very well be that the name would be well accepted for a boy in Australia.
All the best with your name hunt - I know it's hard!