2. The n800 does not have a built-in GPS at all but you can connect to an external bluetooth GPS if you have one.

3/4. The n810 has the options of thumb board or text recognition as well. You don't have to use the builtin keyboard if you don't want. Or you can use an external bluetooth keyboard with either of them. See if you can get hold of an n810 to try out the keyboard: it takes some getting used to but I think isn't at all bad.

7. How often do you want to change cards? The n810 has 2Gb built-in, sort of equivalent to the n800's 'hard to get at' card except you can't change it at all.

You missed: the cursor rocker switch on the n810 is only accessible when the keyboard is open, and the n810 is slightly smaller.