After skids posted his gearing chart I did a bit of work to simplify mine and merge it with his ... see if this makes any sense, and let me know if it helps ...
pchweb.co.uk/desmodue/duc gearing (skids).xls If it works, and anyone wants to contribute some data, just shout.
(If anyone has any other useful dd-docs that arnt too big, I can post them there too)