It's difficult to say unless you've studied at both places. Monash is a highly regarded university though, it's in the top 100 universities world wide (according to The Times Education Supplement) and it's in the top 8 in Australia. VU doesn't enjoy such a reputation. But, that's not to say that VU scores are entirely meaningless, either.
In the end, it is probably reasonable to say that your cohort will be much stronger in terms of academic performance and even without grading curves, your performance is usually judged in relation to other people's performance. This means that it probably won't be as easy to get HDs. It doesn't mean that you can't get them though or that you shouldn't expect to get them, it just gives you an incentive to work harder. If there is a better standard at Monash, they wouldn't let you in unless they thought you could meet this standard.