I wouldn't have a problem with that many panels. All it does it ensure your inverter runs to max for longer. It will run higher than 5kw anyway (and will probably actually have an output closer to 5.5kw). So by throwing 6.5kw on the roof you will get a higher output all day, and max output of up to 5.5kw during peak, so you would assume that a 6kw system would go to at least 6.5 (probably higher) so 7.2 kw would not be a problem. They just serve to increase peak time. Also the sun would not be as intense in Radalaide as it is up here, and plenty are doing it up here.
Plenty are doing it, I wouldn't have an issue. My main interest would be what brand is the inverter. My two SMA inverters are still going strong, but Im sure they are others that are good.