The A380 does the job. The A340-500HGW as well. Just got to pick the right one depending on the demand and competition.
But, most of all, pick the plane that suits the majority of your demand, not only 2 or 3 prestigious routes.
Last GW#2, some alliance fellow based in Australia used a combination of 737, A330 and A380. Did wonders, always sticking to the top 20. Because above 8000nm he was unopposed and the demand was high enough, his A380 were all filled up to the brim, printing loads of cash.
But do your fleet structure, cashflow, profile, etc. allow some space to such an expensive bird? You need to check. But usually, ULH is the last area in which one expands.
Now, about your potential new base. It depends how well your competitors is doing. What do you call "well established"? covering all the demand doesn't mean he's doing well. How much cash does he have in reserve? What is his cashflow? His margin? What kind of fleet does he operate? How well done is his scheduling?
The basic idea would be to go first on the routes where there's clearly money to make: either he serves it with a bird you can undercut (you beat him with frequency) or he doesn't covers the whole demand, or you go for routes he does not fly yet (too far away for his fleet).
You'll always have more chance, at least initially, on thicker routes. But spread your apples, check what counter-attack he might put up, etc.