If I recall correctly, back when we were discussing whether lifting the ATAR cut-off for all courses to 80 was a good thing, someone posted a nice graph which showed people's first-year average scores plotted against their ATAR. It had lots of nice, pretty colours (yes, that's what attracts me to graphs), and I think it showed that while the average marks of the 99+ were definitely higher than that of the 60's people, there actually wasn't all that significant an increase until you got a bit into the 90's. I would imagine there to be a positive correlation between ATARs and uni scores to an extent - but I personally think the variability in uni scores for a given ATAR 'band' weakens this a fair bit.