I donot think it is fair to compare these two bikes, it is totally dependent upon what your needs are.
The reason why i ride a gs, is very simple, last year on a 5000 odd km 10day trip through Botswana and Namibia, i decided one morning at 08:00 i am returning to Pretoria from Luderitz. Got on the bike travelled 900 odd km to Upington, the next morning early i got on the bike and did another 800 to 900 km to Pretoria, upon my arrival in Pretoria i was ready for another trip. The question in now, at the age 50, would I have felt the same on a different bike, i am not so sure about this.
I am not ridding a gs to push the limits on technical ridding, i do because I would like to get from point a to point b comfortably and not being concerned whether it is dirt or tar....... 
There much assumption here that at 50 you are, for lack of a better word, physically disadvantaged. And what is the relationship between age and a bike? You could be 25 and may not ride 800kms. I have done 1500m in 14 hours on a V-strom. Was it the bike, I wonder! 
My point is to argue entirely that because a bike is advanced technically and therefore enables one to ride long distances is false reasoning. Please spell out clearly the technical aspect that makes it possible to ride long distances. 
Ek wil ook nou nie somer net die thread hi-jack nie,, maar om van Luderitz Upington toe te ry en van Upington na Pretoria die volgende dag is nie juis ernstige km's nie, veral nie met vandag se bikes nie,,
Ek is nie bang om lang distansies te ry nie en het onlangs vanaf Luderitz na Upington gery via die Oranje rivier, en van Upinton af die volgende dag George toe, en dit na 'n amper 4000 km trip waarvan daar op twee dae net oor die 700km per dag gedoen was,,
Om distansie op 'n dag te ry is 'n "mind set", 'n Africatwin is nie die gamaklikste nie, maar ek het al met een vanaf George Jhb toe gery een dag , en die volgende dag Maputo toe, en daarna my trip op in Moz gedoen,,,,