... The only real notable difference in terms of candidates is that Monash gives small bonuses to the students in their state.
Another notable difference is Monash cutoff for interstate interviews is significantly higher, like last year a 99.5/94%ile (65/50/71) didn't get a 2nd round interview whereas a 99.0/92%ile would comfortably make Unsw. Once you are not let into the interview round it's moot point whether difficulty is approximately the same.