your hsc assessment marks would be affected by the ranks. but remember the assessment marks only count for 50%. the other 50% is your hsc marks. if someone does beat u in ranks it would only mean that he'll beat u in the hsc assessment mark but not necessarily the hsc mark. your final hsc result...
went to the info day. the minimum stat score is 150 this year. gettin a high stat does not rank u higher. as long as u get over 150 ur uais are ranked.