Hi Santrix,
I had a test ride on an 800GS just recently, and loved it -lighter than my 1150GSA, and a lot easier to move around etc. Couldn't believe the cornering on the 800 too, -might be just me, but it was a matter of point and go -it just held the corners a treat.
So, all was going fine until I ran out of filling stations, none for the last 30 miles, and with 5 miles left showing on the clock it ran out of fuel...embarrassing or what -had to walk to next garage etc etc.
So, I have a good read of all the info here on the 800's -only couple of doubts I have ( as I do love my 1150, but age beckons , that's me & bike !!), are how it handles with luggage, tent, panniers etc, and I found the engine a bit peaky/jerky on the throttle. Maybe I needed more time with the bike , as I only did around 130 miles. I would be a little cautious with that kind of throttle response on gravel and mud.
But, it is certainly on my list for my next bike in 18 months or so.
Final things, tubed tyres ??? and water cooled...a chain I could just about manage to live with !