Here is some more information to confuse you more (I just bought an N810)

The virtual keyboards are fine for filling in forms with just a few words, the slider is much better for anything much longer (like this posting), but you can get many USB or bluetooth keybards for either. I have a flexible roll-up full sized USB one for mine.

Some of the apps seem to be optimized for the button layout of the older 770/800.

An external GPS is probably better for automotive use because the antenna needs to be in the window for good sky view, therefore so does the N810's internal GPS. The map options of the 3rd party (and free) GPS appa are real good however, and you can pre-download a set of maps for an area you want.. So far the GPS apps are awkward to use while driving unless you got your routes all pre-loaded as well.

The N800 has an FM radio, if you care.

The N810 is slightly faster,

The hp power is low, but it appears to have nothing to due with headphone impedance, just the overall effeciency of the headphones. I just tried several sets I own and my 60-ohm Koss KTX/Pros do as well as or better than the many 16 to 30 ohm earbuds I own. The funny thing is that the sound from the built-in speakers are amazingly loud and good for what they are (tiny).

Even though they claim you can only put an 8-gig mini/micro SD in an N810, I'll bet you can put in a bigger capacity one once somebody actually starts making them, which I've heard might be real soon.

A lot of people who have owned all, seem to prefer the overall size of the N800 or N770 better. They think they are more rugged.

All that said, I do like my N810, but maybe the N800 could be better for you.