Hello! I just finished my speech pathology degree 1.5 weeks ago literally hahahaha! But I came from the undergraduate degree (Bachelor/Honours) and not postgrad. Most of my peers who are doing postgraduate (Masters) did the "Bachelor of Health Science" degree previously - which is mainly at the usyd main campus and not Cumberland campus. Why not just do undergraduate straight away instead of post grad hehe? ^_^??
Regardless whether you do undergrad or post grad you'll end up learning the same thing, except Master's is done in 2 years instead of 4. To be honest, I dont think any undergraduate degree would 'help' with what you learn as I'm not sure of any degree that teaches the stuff we need to know?? Maybe try to find something that gives you the basics with anatomy, physiology and neurology (particularly head, neck, brain). I think you can learn linguistics really fast if you practice heaps.
Half of the course seems "sciencey-based" (e.g. like neurology, cranial nerves, anatomy of the head and neck, swallowing problems) and the rest of it is "Englishy" (e.g. speech, language, fluency, voice problems).
Some keywords that might help you find a course to prepare you or give you an insight into speech pathology are: phonology, semantics, syntax, morphology, dysarthria, dysphagia, apraxia of speech, stuttering, aphasia, pragmatics, phonetics, linguistics, phonological awareness.