What spring rate are you running? I'm about the same weight as you and, after switching to 1Kg/mm springs, I still need to crank the preload all the way in to get front sag below 40mm. If I remember correctly my rebound damping is also almost fully in, and my compression damping is about a turn out from fully in, or something like that, mostly to combat brake dive.
In the end though, the purpose of preload, is to allow you to set the resting (or coasting) position of the suspension, dividing the total travel into travel available for compression and travel available for extension. If you don't feel any jolts due to bottoming or topping out, (unless you hit the mother of all potholes of course), then I don't think there's much point in worrying about it (although, if you've got a lot of headroom, i.e. the zip-tie never comes close to covering the full 120mm of travel, you might consider softer springs next time around).
You can then set geometry, either by making small adjustments to sag, or, more properly, by pulling/pushing the forks through the triple clamps and shimming the rear shock, as suggested. That's a compromise too, of course: straight line stability vs. easier turn-in (and more feel for available traction, I believe, as less mechanical trail makes the effects of the tire's pneumatic trail more prominent, and the latter peaks out a bit before the side-force peaks out and the tire starts slipping, thus providing a sort of early warning). In general, I think, it's best to have an idea of what you want to improve, before attempting adjustments.