I have both bikes. The 1200 adv is great cross country, two up,does well on dirt/gravel roads. I really like the ESA. It can do just about anything. Long mileage days comfortably, it can do more stuff off road than I would want to try with it....
The 800, in my opinion, is a great one up road bike that can do pretty well off road too. I can pull 600 mile days easy on it, (granted I did replace the seat)........ and it does pretty aggressive off road really well.....I would say a true 50/50 bike. I have ridden it fairly aggressive on the road with absolutely no complaints....same off road.
Mainly hwy use with 2 up, the 1200 is hard to beat...... about a 50/50 mix one up I prefer the 800.
14 1200GSAW, 12F800gs, 11Griso, 10XR1200, 08S2R1000, 90BMW K1, 77Boneville, 76R75/6