Test rode both but at the end of the day I knew the GS would still make me smile.
For the trip:
There more farkles out there for the GS since it's out for 4 years. I think you'll find more BMW dealers on the road anyway if something happens. For the comfort I'd still buy an aftermarked seat (even to lower your sitting position).
It's WAY easier to shut the ABS off on the GS and it has a better mileage (4l/100kms vs 6l on the triumph).
I know that the sound of the XC would drive me crazy on a long ride (don't like the whistling sound of it... each one his tastes
). Anyway the GS feels more offroad oriented to me and having the tank under your seat is a great plus for that kind of aeria.
For the "BIG Lost-Rider Fuel Tank". It's from Touratech and costs about 1000$... I'd rather buy some extra fuel cans that you bold on your bags. One other good reason for that would be that you have no crash bars out there (correct me if I'm wrong) that would fit that Big Fuel tank... and I think crashbars are one hell of an important thing on these trips.
Wow... reading all these points I can't remember why I had a crush on the Tiger
. Anyway each bike should do the job but since you're in Parallel Universe it's always a bit hard to stay neutral :o)
Oh and my personal 0.02 (yeah that one is personal): I'd buy a used one that has already some farkles on it. I don't trust all these electronics on the new ones that have some problems we don't even know of yet... Oh yes for instance that you can't completely shut of the ASC...