Just a correction, there is no 6 year degree.
The BPsych at Monash is a 4 year degree that lets you do an alternative exit after 3 years instead (giving you a Bachelor of Psychological Science) if you either don't want to continue into the 4th (honours) year or fail to meet the requirements to get into it (70% avg in final year psych subjects). If you take the alternative exit, you can apply for honours in the future.
Otherwise, you can complete APAC psychology majors in BArts or BSci at most universities that offer it I think? Then you can apply for honours after that - these often have higher requirements though. These degrees let you explore multiple areas of study and if you find you don't want to continue psych, just alter your course structure accordingly.
To become a psychologist, the absolute minimum is 3 years of undergrad (APAC accredited major), 1 year of honours (or equivalent graduate degree), then the most competitive route is a 2 year clinical masters or 3-4 year clinical PhD.