Curious why the 1200GS vice the 800GS since your comparison is the 800XC. Ridden all, esp the 800's and different animals each!
What the 800GS does on the trial (yes it does need a new suspension) the 800XC crushes on the road (the triple is amazing). Both are very capable in the aspect your looking at.
1200GSA is a different animal, very capable but so far from the scope your looking at w/the 800XC. Each is very easily capable on/off road on trails/roads/sand/etc. Just not single track bikes.