If you want to know what DPI to set to make a map and what to set it to for printing the map then I would suggest you read my lil ole tut here.
[Award Winner] Bitmapped Images - The technical side of things explained.
(specifically, bottom of post #4)
If you want a high res middle earth then I have this one which is from the ME-DEM (Middle Earth Digital Elevation Model) group of which I am one of the admins. That's a free map of V1 and its very high res.
January Entry: Middle Earth
V2 is in progress. If you want to know more about this then its www.me-dem.org