Very interesting... I am working on a similar kind of project, mapping out a whole world using Photoshop and Wilbur, like you. And I too began with the continental outlines/sea mask, and decided to build a height map in Photoshop for further processing in Wilbur. I considered using real world data, as you have so effectively demonstrated, but ended up going with my own model based on rendered clouds in Photoshop, with lots of masks and level adjustments.

In any case, that part is different, but the erosion part is very much the same. I'd love to hear what settings you're using for erosion. I have experimented with various different "recipes", using both precipiton erosion and incise flow, noting the settings each time. But so far I've only found one set that gives me the kind of results I'm looking for. The results of your process look rather nice.

Regarding the resolution you've chosen, I'm assuming you went with those figures to be on a similar scale to the next generation Blue Marble imagery? I made a similar decision to go with a base 21,600 x 10,800 world map. It's big, but not so big as to be unwieldy. However, I found that the erosion produced by Wilbur does not scale properly - the valleys carved by incise flow end up being far too big, and not detailed enough. I later read on another thread by Wilbur programmer Joe Slayton that the in-built "resolution" of Wilbur's erosion is 1 - 50 metres per pixel. Blue Marble is roughly 2 km per pixel. That's a huge difference in scale, but it's simply not feasible for a world map to be 50 metres per pixel. A roughly earth-sized world would end up being in the realm of 864,000 x 432,000 pixels - ten times the size of the already unwieldy full resolution of NASA's latest Blue Marble!

I have decided to compromise, and go with a full resolution of 86,400 x 43,200 - handily maintaining compatibility with full resolution Blue Marble - but split into continental parts to make it feasible to work on even at that rather massive resolution. I've found that Wilbur works best with pieces of 9,999 x 9,999 or less, so I have split my continents up into four to six parts each, overlapping as you are doing.

I'll be following your project with interest. I'm working on some posts about my own project to post soon, which I hope you might find useful too.