Took the new F800GSA up to Palomar Mountain (California) today via Nate Harrison Grade. All pretty healthy uphill, gravel, rocks and areas of old asphalt. Had to ride fairly conservatively since I wasn't sure how the stock tires were going to perform...and they did OK, but didn't push it for fear of losing traction.
Offroad, I usually ride a 210lb 70s 250 Husqvarna. Big difference :)
When I purchased my R1200RT two years ago it took about 6-7K miles to get used to it. I suspect the F800GSA will take some getting used to as well.
Overall a fun little trip, but I was happy to get back on the pavement because of those stock tires. Not sure which ones to replace them with.