Wilbur can only generate data at a detail level proportional to the image size. The incise flow and precipiton algorithms generate their most plausible results at between 1 and about 40 meters per pixel and the rendering algorithm gives nicely visible results in the same range. Unfortunately that means that a Wilbur map would need to be on the order of 25,000 pixels wide and high for a 1000km wide map to give nicely plausible results. You can do that with the 64-bit version, but you'll need lots of memory and patience. A 25k square map takes a bit more than 5GB to represent and about the same amount for each of the undo levels - some algorithms require several work surfaces to do their job so it's just not practical at this point in time. Give it a few years, though...