I've never tested the K series.. but have been on the R1200RT.. VERY smooth, but like you.. just wasn't better enough to warrant the payments.
I caught myself playing with all the toys while I was test driving it.. checking out the computer, playing with the powered windscreen... then thought "HEY dumass, pay attention you're driving a motorcycle!!"
I did play with the widnshield to see how it blocked rain at different levels. I had to pay attention because it was so different.
The lack of front end "dive" was nice. The linked brake (front) was cool.
The shifter and brake being so far back and under was strange to me but I could get used to it of course..
I did NOT like the RT's fairing mounted mirrors AT ALL. They would have to change.
I liked the modular top case.
I wasn't all that impressed with the controls. Some push in, some push up. I had to move my hands to reach some of them.
The shifter and brake felt flimsey as did the tiny grips. I am sure they are strong enough but they felt small.
Transmission shifted same as the Harley, maybe less distinction between gears but it was smooth.
Engine reved quicker and there was noticably more power but it was not a "Oh wow" type of power.
The one most notable negative I did notice was the "feel" was not what I would call "stable". It seemed to be rangy. A ripple gouge or bump in the asphalt was felt immediately and it disturbed the bike.
All in all it was (I know you are going to hate this Bob) "just a bike". I half expected something that was going to be so spectacular it was going to make me sign the title over on my Ultra and make a quilt out of all my Harley T-shirts never to turn back to the dark side of American Engineering Ja!. It just wasn't the case.
They are nice bikes for sure. Lighter, different seating position, more power but in the end they do all the same things as Harleys do. Somethings it does differently but the end result is the same.
Would I like to have one, sure and I might get one. My Harley is almost paid off and I have room in the garage.