No, you need a university that is good in both faculties. "Good overall" is one of those stupid expressions based on the opinions of those who aren't involved - ie those who don't matter. If you go to someone in the field, like an employer, then they will know which universities have the good faculties of interest. The other bits (like the irrelevant faculties and the student associations) are not important. KPMG doesn't care if you've got a dodgy Engineering faculty, they only want to know about the Commerce and Law faculties.
This applies to overseas employers as well, as long as you are looking at large firms or academic positions. Obviously the smaller companies will have less exposure to Australian academic performance, in terms of knowing which uni has the good lawyers, accountants, etc.
And lastly, Go8 does not automatically mean good for you. Imagine this scenario: two students study Nanotechnology (yes I know I'm using my own course, shut up) and get the same grades, but one is UTS and one is USyd. Here's where the Go8 graduate is definitely NOT going to make the cut, because UTS has the international reputation for Nanotechnology whilst USyd has bumpkiss. There are other examples, but I don't have them at hand. The point, I guess, is that you should never make stupid generalisations about prestige because they are just as often WRONG.