You might also look into the Battery Grip. A bit pricy but it houses two batteries so no switching is needed and if I remember right will also let you use AA if you need to in a pinch.
I shot a wedding for eight hours. I shot 1600 frames plus about 5 short video clips (IS on the 70-200mm but mostly using the 24-70mm). I had one bar on the battery left at the end of the day. I think that is pretty impressive but I am definitly going to buy another battery (if I can find one in stock) because I really don't like the idea of getting near an empty battery. Especially at a wedding,
That's something I also thought; 850 on the manual sounded very few. Well, I did buy another battery anyway; it wouldn't be very good idea to ask the bride and bridegroom to wait a couple of hours until I'll get my battery charged ;)
Haven't measured mine, but both the Live View (if you use it) and IS are good battery-suckers that you might not have had on the 40D.
40D actually has Live View, although I hardly use it. Don't have IS lenses either. But I guess I just have to go and buy a spare battery anyhow :)