i have done this upgrade so heres a list of differences:
u get track id, java 7.5 (updated from 7.4 on
k800), different themes (but still doesnt support flash menus), photofix function (which only does what you can do in photo dj just automatically) and thats it i think.
also
k810 firmware is supposedly faster than
k800 but i havent noticed a difference and due to the keypads lights being physically slightly different on
k810 only the keys light up and not the thunbstick/softkeys etc.... unless you go into the camera then it all lights up.
theres not really any major changes on the
k800 firmware and i only did it out of curiosity so its up to you really