N800 speed was 330MHz with OS2007. OS2008 changes clock speed on the fly depending on the CPU load and this makes it identical with N810. The top speed is 400MHz on both N800 and N810. So, there is no difference as long as you install OS2008.

USB host mode works also on both devices with OS2008. Just remember that N8x0 is OTG compliant, meaning that when host it can supply only 100mA of current. (Though, there seem to be some headroom made up to 200mA. ) This means most low power devices work, but not high current draw devices, such as iPod that charges itself from the host USB port.

If you do not have OTG compatible peripherals and suitable cable, you need to do switching between the modes (OTG and host) in software. There is a thread something like "N800 host mode experiment" where you can find more info how to do this.