I know coming from both the RT and the GT that the pillion was far more comfortable on the RT by a long shot. The RT seems to have better wind protection and doesn't buffet her around as much. The GT may be a bit more narrower than the RT too, so maybe that RT extra width shielded the wind off her?
The GT is faster, of course, but I think the RT handled a lot better in the twisties due to the less weight advantage it had and maybe a lower CG too. I've often though that odd rotation (inline of the boxer engine crankshaft) attributed to better cornering over the GT. If you eve rode a boxer, if you rev the gas it sort of torques over to the right side easily. The GT you have to fight it more to get it leaned over.
Sadly, my GT seems to sit a lot more as I favor the much lighter weight of the S1000RR now for some reason. For touring the GT is nicer for a solo rider - if it wouldn't break down or get vandalized and sit hundreds of miles away in some shop awaiting to get fixed as it was prone to do at times. Least the 3 year warranty always came to the rescue but man, did it like to sit in shops a lot.

My old RT had almost 100,000 miles on it when it got traded in for the GT. Wish I could have kept it as I never had a major issue with it although many reported oil damaged clutches (bad tranny seals that got hard and leaked) and a flurry of final drive failures which seems to have quieted down a it in the last 2-3 years. But that boxer engine was pretty much indestructible and easy to tune and work on too.
In the 1600 sale's video, I noticed the pillion sits very high or she is a lot taller than the driver and can almost see over the top of his helmet. Dunno, but I suspect it won't be favorable for the passenger over the wind protection the RT offers over the GT series. Guess we'll see when it comes out and gets some pillion reviews on that. I can't see it beating the creature comforts of the 1800 Goldwing for passenger comfort though. They are pretty spoiled back there and some can even fall asleep.
Mack