It's been a while, but I was exporting tiled images to produce a 30000x15000 pixel map in the end. I manually aligned them in photoshop. I believe that each tile was 5000x5000 pixels as I could reliably export that size, though my memory may be off and they may have been smaller.

If you look through my early posts about 'Abebe' and most of the posts in this thread that I started (I probably sound grumpy) that mention Fractal Terrains, you'll find my notes. I don't have time to look now, but I hope that gets you started.