I got back on a bike after 25 years, passed my test (I last rode in the days when you could ride a 250cc bike without a full licence) and bought a 1100GS the next day. I put 20,000 miles on the clock in 11 months. Yes, it was big and I dropped it three times while pushing it about

but it was just so easy to ride and so comfortable on long journeys. In my opinion, go for the big GS if you want to try it.
Having said that, I am about to buy an 800GS (this Friday

). I intend to learn and use off-road skills and think (admittedly based only on my road experience with the 1100 GS) that the larger GS will be too heavy for long distance rough roading with luggage and spare fuel.