I had private health cover prior to my diagnosis. It enabled me to choose my surgeon but he also practices in the public system - he has an excellent reputation btw.Many breast surgeons work in both systems but in the public system you cannot choose your surgeon.
I have talked to others who have used the public system and they have been delighted with their care esp the follow up care by the nurses after discharge.If I have a complaint about my private hospital it was the absence of follow up care after I was discharged - the care whilst in hospital was good however.
Private radiotherapy has a substantial gap payment not covered by insurance. My gap on 16 rounds was over $2000 , many have more treatment cycles than mine and have gaps of $5000+.You can blend private surgery and chemo with public radiotherapy which I would have done given the hindsight.
Re preexisting condition rule - I think you would need to research that very carefully with the insurance companies.
My rationale for going private was that I had had private cover for many years.I’d probably go as a private patient in a public hospital for surgery if there is a next time as gather nursing care here is excellent and definitely public for radiotherapy.