10kg is plenty IMO, Unless you re likely to encounter big Yellowfin or are in Sharky waters, Mackies will have a couple of big runs then turn over, whilst longtail and mack tuna go hard until the end.

 Well today we were out catching 5kg salmon using 30lb braid, clips, swivels and leader and lost 7 lures with the fish breaking clips, snapping leader, and braid, the bazar thing was the line was not always breaking at the knots...

THEN, $150 later, discovered that the drag was done up tight....

Set your drag properly and you should be fine. Remember people catch BIG fish on light line, you just may have to follow them around to tire them out if you get onto something big.

If you are planning to fish from Steep point north in a boat then you want to consider 60lb minimum unless you want to serve up fresh fish meals to the resident sharks. Skulldrag is the name of the game because if you stuff around they will beat you every time

I agree with Carnarvonite go heavier.  I regularly fish 30 pound down here for and rarely bust off.  Also up there fishing in shore the fish go to the coral more. I had countless bust off on spangos etc in shallow water where they drilled me into the coral. Then there is the shark factor plus you might hook a billfish. 

Yep 30lb fine for targeting macs. (not too much in the macs) Although the big YFT if you hook one will test you.
Being sporting is great however if you really want to land big YFT heavier/less line is better than lighter/more line. (if you don't stop then quickly it turns into a long fight)

Bottom fishing 50lb min unless you are prepared to be very sporting and loose a lot of rigs and fish.

 Thanks guys