Try to do IREX questions dating back 10-20 years ago as well as the modern questions.
In my experience, the older questions tended to be harder and made one think more carefully than today's questions. If you can pass those, today's IREX questions should be a dawdle.
However be aware that Australia's charting standards have changed over time to become ICAO compliant and there may be some questions relating to approaches that no longer exist e.g. questions on DME descents. Also older questions may not cover GNSS content or procedural requirements.
Just my two bob's worth.