I have them both. If everything is up to date they would have the same software. Since they use the same processor speed is not going to be much different.

I haven't noticed much of a difference in battery life so all things considered, If you are not going to be traveling much with it the N800 is a better value and as tgalati4 said, it has two, less expensive SD cards.

However, if you are going to carry it with you a lot and plan to use it outdoors at times, the smaller N810 is easier to pocket and its trans reflective screen is easier to read in direct sunlight.