If you're going to "bash over the rocks" go with the 800. If you want a smooth street rider that you can tackle easy to moderate trail work/off road, go with the 650. In my experience riding both, the 650 rides like a good street bike. It handles well in general, the suspension is comfortable, the brakes are more than adequate, the low end power is outstanding, and it corners like a dream. The 800 is a great bike as well, but definitely rides more like a dirt bike. It has a stiffer suspension, it's torquey and pulls quite a bit more, and sits notably higher. I also noticed that, IMHO, it takes notably more work to corner. Both are outstanding bikes. While I respect Coon's opinion, I don't think anyone who does their research on which to buy is going to regret it either way. If you want a street bike to play with once in a while, buy the 650. If you're honestly planning on riding some real trails or do some crazy around the world remote area camping trek, buy the 800. My personal call was to get the 650 for my daily riding, keep my XR (the red beast) for trailing and pick up a KLR for a better cross over in the future. There you go, that's my opinion and you know what those are like.
"In the end victory goes not to the swift, but to the stubborn"