Ok I'll outline this plain and simple.
Natural Ability will only get you so far, probably anywhere up to 90, but not beyond it. This is reffering to pure natural ability. This is probably what I relied mainly on but even I had to pull myself out a little before the HSC exams and actually read through the revision guide once. The only thing I put a bit of sustained effort (few weeks towards the end) was 3U maths, and this showed, as assessment mark of 57, HSC mark of 73. I acheived my 86.90 UAI with 0 complete past papers done in any subject, only looking at/doing homework maybe once a fortnight, minimal class attendance, and normally a few hours revision before a test. Now see I still did get far, but it's not great. What happened was in some of the exams say Biology and Economics, I felt I knew everything in the test, even after I completed it, but I received exam marks back of only 86 and 88 respectively. I can put this down to not knowing how to answer the questions as they wanted. I had the content knowledge, but the HSC also requires the knowledge of how to structucture your responses to include everything they want. This is where natural ability will not help you as the only way to know this correctly it from studying past papers and exemplar responses.
Thus;
Hard work will get you further, if you are in a study pattern which at least involves 5 days a week of doing extra work (even if it's just homework), you can acheive up to 97 without that much difficulty. How well you do will of course depend on how much effort you do put it, but if you simply study some exemplar responses and past papers, you can be assured of doing fairly well.
Now, to acheive anything 97+ will usually require both natural ability and motivation/hard work. It may be avrying quantities of each in different people, but you will definatly require both to get this high, no one quality alone will get you here, despite what people say.
P.S. 1000th post!