The maximum you can pay is 5 lots of $50000 per phone call so that is a total of $250000 plus the credit card fees. If you owe more you make another phone call or two until the bill is paid.
Westpac for me has been so easy....cash a large cheque into the card on the day the tax is due then go back from the bank to make the phone calls.
Citibank is harder because if you put a cheque deposit in thru Australia Post it takes 6 days for the funds to clear into the credit card limit.
American Express Ultimate won't allow your account to go into credit so I phone the funds thru every 3 days.
You need to have good sized credit limits to pay large tax bills.
You can use NAB as it takes 3 days since it's banking institution.