I have a P800 and have played with the P910i.
First off, OGG plays fine with a freeware player
The screen on the P910 is much better than the P800 but its still a budget screen so won't be as good as a PDA screen although its still viewable in full sunlight.
It won't last as long as your Nokia - don't forget it has to power that huge screen, lol. I find its alot like a laptop, it'll go down quickly if your doing things with 3D programs or listening to music loud (or actually using it as a phone, LOL). I have to charge my P800 every 2-3days. I just shove it in the dock every evening though.
Outlook - yup
File viewers, I'm not sure if this is different on the P910 so you'll have to check, but the default viewers on the P800 are basic
you can get better ones though.
You can put pictures fullscreen in widescreen - also you can setup a button to skip through the pictures in that folder so its great for showing people pictures
By default you can only use the funny 3 format (I Think thats it) and the player is - basic. But there are better video players out there - although alot of them don't support widescreen video (kinda defeats the point of buying a phone with a big screen, lol).
I've seen eWallet software but never used it.
I'm sure you could get some kind of list software - failing that, use some spreadsheet software creatively.