I have done two up touring on a Thundercat, ZX9R (two of 'em) ZZR1400 and now bought a GS, but yet to do first tour.
Before buying the GS we tried a Tiger as well, out of all the bikes prior to the GS she prefered the Thundercat for comfort - even over the roomier ZZR (which even had a Tony Archer Gel seat)
She had no issues with any of the other bikes except the Tiger which ahd a small pillion seat and made her feel like she was perched right on the back of the bike, she really did not like it.
She liked the GS on the test ride, and I find it rides very well two-up even in stock trim, on longer runs I found it getting a bit tough on the butt, but £80 for a TA rework to add a bit of padding to the seats seems to have fixed that.
I am really looking forward to doing some proper long runs and tours this summer, the thing is roomy, fast enough and fun on all types of roads and in most weathers.
Some here really rate the GSA over the GS, I only rode the stock GS and liked it, coming off sportier bikes I did not fancythe extra weight, but perhaps you should try both.
One last thing is some passengers feel much safer with a top box behind them, I have never understood why when all the danger is from the numpty's pulling out in front of you, but if it helps get her onboard then why not
