Bealzebub makes two very good points:
* taking the best class of travel you can afford; and
* breaking your journey.
I've lost count of the number of times I've been asleep after takeoff on the the night flight from LHR (having changed my sleeping patterns well in advance), only to awaken four hours later to find a darkened cabin full of slumbering people, so here I am, bright-eyed and bushy tailed with nothing to do for eight hours before our pit stop.
Why is it that I have to drag myself out of bed after nine very pleasant hours of weekend sleep, but I cannot sleep on a long haul flight? I can even doze on the Underground, which must be the closest thing to Y class or live animal exports.
Splitting your trip means two 'Thank God' experiences. You say you're a tall man - there's nothing better than stretching out on crisp linen sheets, and you'll be in a better frame of mind for when you reach the fair shores of Australia and East Australia
If I had the choice, I'd hop across the States, have a furlough in LA, down to NZ, across to Australia, and then dash for home.