A critical point with large maps and Wilbur is to not do everything at once. If you want a 14000-wide map, start with a 700-wide map (or even 350-wide) and do noise/basin fill/precipiton erode; simple resample by 2 in each dimension and cycle again. Repeat until desired size is achieved. http://www.cartographersguild.com/sh...ad.php?t=28052 was done with this technique (the full-res version has moved to http://www.fracterra.com/wilburiax.jpg since the article was written).
If you set the size for 350, loading your full-res land mask as a selection in Wilbur will automatically downsize it to the current image dimensions, allowing a single mask to be used for all sizes. Cleaning up edges is a good idea, so loading the land mask after each resize, inverting it, and setting the sea area to your desired low value will clean up the square edges.
Another good tip with Wilbur is to pull the continental maps out individually and reproject them to an equal-area projection. Wilbur's erosion and river-finding algorithms assume a planar basis and trying to do everything in an equirectangular projection will get some awful high-latitude polar artifacts.
I was looking back at the earlier posts and I saw that you had posted a couple of terrain masks. After popping out the data in Photoshop, resizing the masks to 512x512 and then pushing things through Wilbur starting at 128x128 resolution, I got the following output in about 10 minutes of total time:
ab.jpg
One-handed because I was holding a baby in the other.
I didn't do any special treatment here, just started at 128x128 resolution, scaled the original image to about 15000 in vertical extent, clipped the water to the water mask (I didn't keep the subsea features), and then did the "noise/basin fill/precipiton erode/simple resample by 2 in each dimension" for 128, 256, 512, and 2014 sizes. I didn't enforce the original water mask (load land mask, invert, set to -1) until the 512 resolution size. At the 1024 size, I pushed water down to -1000 and did a little precipiton erosion to wear down the coastline a little. I also added the river overlay to show the major waterways.
The fun thing about Wilbur is that this process works equally well with just a 2-level mask ("coast" and "mountain") to show the major landforms. The hardest part of the problem is getting enough roughness. If you have specific rivers that you want to be present, it's possible to do that was well by having a separate land mask with the rivers cut out from the coastline. Load that mask and do a fill basins before adding any noise and the rivers will become the low parts. If you want specific watersheds, you can rough them in by using a selection of the outline and a linear gradient with operation=Add pointing upstream.