If you are slide baiting. 1.5m if the swell is up a little, and up to 2.5m when it is nice. Keeping in mind that the fish will drag the mainline across at will.
Off the rocks, 3m..... for me, when it is longer, it can be an issue under ledges when it gets out, or in the weed at your feet, but that is fishing water that is in the 3-10m bracket. Kingfish in close generally feed off the surface.