I've ridden every GS from R80G/S to 1200 and reckon 1100 is best. Best build quality with enough power and decent brakes and suspension. When the original shocks are tired, consider a swap to Wilbers units.
Had my 1100 for nine years now and still love it and enjoy riding it. It does everything I need in a bike. Perfect motorway mile muncher will easily do 800 mile days. I've also got a Wunderlich Erco seat, raised bars, larger screen and 41lt tank.
Fit a set of TKC and you've got a great off-roader which I entered the 10 hour overnight Dawn to Dusk enduro. Also fitted the Touratech hard parts to gearbox and front forks.
Combine the two attributes and you have a machine capable of a 10,000 mile round trip to The Gambia and back.