Bit late, but never mind eh?
Just my brief thoughts as the other test rider....
I've always liked the GS, and haven't ruled one out as a future bike. However it's not as clear cut as it once was.
GS/GSA twin cam - cracking engine, I really loved it. So much grunt off tickover, sounds good too. However I did have it bouncing off the rev limiter on more than one occasion, especially when chasing the K1300R - it didn't get away that easily! Great road engine.
Riding position was great, loads of forward vision. I did notice a lot of buffeting off the screen on the Adv, I tried adjusting it a bit but couldn't get it to an acceptable level. Maybe more time to play with it would find a solution.
Handling - The GS definitely handled better than the Adv. Both steered quickly enough, very easy to get it over. My problem with the handling was how vague it felt. I've ridden both the R1200RT and the R1100R, and both have more feel. I was disappointed with the feedback - maybe it's something you get used to?

I was also disappointed by the handling of the Adv compared to the GS - I really like the Adv, but I felt a little disappointed in this area.
So the GS hasn't quite won me over - in fact, IMHO the RT is a better bike. I'll need to try a Tiger, and get a decent ride on a KTM Adv.
As for the K1300R.... again a bike I really liked (especially in the orange colour!) However, I was not impressed. For all of it's claimed power, I found it lacking in the engine department, and it really didn't feel any quicker than my old Fireblade. It did howl nicely when I gave it the berries though....
I didn't find it any more confortable than my (modified) Fireblade. Another disappointment.
As for the handling - I thought it was like sitting on a brick wall. Mega stable in a straight line, but a bugger to turn. I was pleased to get back on the GS!
So of the 3 bikes, the K1300R was a let-down.
The GS's were good, and I enjoyed them a lot. Of the 2, I preferred the GS over the Adv, it just handled a lot better. However, if I went for a GS, I think I would still buy the Adv.....
The only concerns for me are the lack of feel, and the reliability horror stories. It wasn't good enough to convince me that it is going to be my next bike, but it's still in the running.