corrections:
b) Both N800 and N810 runs at 400MHz ones the N800 is flashed with chinook or diablo.

c) Both have usb 2.0.

d) The memory issue is a bit muddy. The N800 have 128MB attached directly to the cpu (a solution called package on package), same with N810. However, where the N800 has two full sized SD slots (one under the stand, one behind the battery cover) the N810 have 1 mini-SD, and one 2GB SD-as-chip soldered into place behind the battery cover. In either case, only the 128MB PoP memory can be used for programs, unless the user takes steps to clone the os onto a SD (or in the case of the N810, onto the soldered 2GB).