"On 300k Im saving $1750 month on the mortgage if using your 7%...

"On 300k Im saving $1750 month on the mortgage if using your 7% p.a rate."

That would only be true if you spent $300K at the start of the month so the basis of your calculation is flawed.

"Ive tried to give Coles, office works, the print company, petrol bowser, phone company, etc etc etc cash but for some reason it costs me the same.....why would that be?"

Plenty of petrol stations have a cheaper rate if you don't use a credit card. So $300L per month on petrol and stationery? ROFL.

"And if there is a transactional cost I can claim it back as a cost/expense so makes no difference to me."

Only on business items and tax deduction don't make things free you only get back the tax component. Another misunderstanding of basic accounting on your part.

"I spend between 200k and 300k on the cc each month."

$3M/year while spending all day on HC? ROFL.