Craig,
The line strength depends on the area you are fishing in.
If there are bommies and coral reef go for at least 65lb braid or 50 lb mono (offshore 1700 and some areas off Fraser).
If there are no reef structures then 50lb braid and 40lb mono is sufficient.
I have seen reds up to 18kg landed on 35lb mono but you have to be an experienced angler with matching skills and good rod and reel.
I have only ever used 40lb platypus platinum with 70lb leader to chase reds and have bagged out a few times over the years but where I go the bottom is only open rubble country and the reds can be played without fear of bust offs.
Cheers
Barry