If you have a 64-bit version of Windows, you might want to download the new 64-bit portable version of FotoSketcher (available here: http://www.fosshub.com/FotoSketcher.html or here: http://www.fotosketcher.com/PortableFotoSketcher_3.20_x64.exe).
Processing speed is roughly the same as with the normal 32-bit version of FotoSketcher, but much larger images can be used without encountering 'out of memory' errors.
I have successfully tested with a 12 000 x 8 000 pixels source image at 300 dpi. Rendering was pretty slow though ;-)
Don't hesitate to let me know if you have any problems with this 64-bit version.
All the best,