I seem to remember the firmware upgrade fixed a lot of that "problem" (not a problem for me, maybe being outside it never over heats?)
Anyway, on the subject of 800 vs 900:
1) 800 is smaller (maybe a good thing)
2) 900 is bigger (maybe a good thing)
3) 900 zooms further and has more power, plus light shaping options.
4) 900 doesn't need the "5th battery" add on pack to cycle faster
5) Menus are easier on the 900
6) 800 doesn't have that bloody menu wheel that leaves a mark on your forehead.
7) You can't buy a 800 new and 2nd hand they seem to be very pricey still.