http://edc2.usgs.gov/geodata/index.php

No secrets in the world--these sources also allow you to place the water level for seas and rivers (For the imaging texture files) appropriatly.

And, to a limted extent in Carrara at least, you can approximate the "real" heigh of various levels.

Quite staggering to an old bloke like me!

I think you CAN do your last paragraph stuff--NOW!
Todays farmers use it regularly!

Brian