I may have posted on this thread last year (can't tell because it's soooo long). Anyway I can safely say that I went to probably one of the best public schools in Victoria and ended up doing alright and we had a few people do exceptionally well.
The generalization that once students get into uni, the public school students dominate over private school kids really isn't true. I have a friend who went to trinity that got 50's in methods, specialist Maths, physics, chemistry, etc and he still does exceptionally well in his studies, having said that, once of my friends went to a public school and the only 40 she got was in psychology and now she is probably one of the best second year pure Maths students I know! She's done 2 third year pure Maths subjects and aced them and got offered a vacation scholarship in topology with one of the best pure Maths professors (Craig Hodgson).
In the end there is disparity but if you get the ENTER/ATAR/etc needed to do what you want and your passionate about it, then you should be able to well. University is a great part of your life since your experience is what you make of it. You go from school where rote learning gets you through and then in uni you actually learn and understand the motivation behind what your studying and each year becomes more interesting than the last. I personally am addicted to the experience and definately want to do masters. Trust me you don't really learn something until university.
When I'm a parent, I would probably opt for a good private school if I can afford it or the selective schools or the great public schools.