Funnily enough, I purchased my FJR from the local BMW dealer... mostly because I traded my R1150GS for my FJR and they are ALWAYS buying those things because they sell dead easily. Anyway, my final decision came down to a new K1300GT and the used FJR. I sat on both and decided on the FJR.
My reasoning? Well, the K bike was awesome and was REALLY comfortable. It was loaded to the hilt, so I was looking at a tad over $20K for the bike. However, money wasn't the driving factor; it was simply the fact that when I sat on the K bike I really felt like I was sitting
in it, rather than on it. The dash came way up in my sight lines, and it seemed like there was acres of empty space between me and the dash. To me it felt more like a touring bike than a sport bike... and while I'm no spring chicken (at 38) I also don't think I'm old enough to put away the sport bike toys just yet.
The FJR provided much of the same on paper as the K. Power was pretty much a wash, weight is similar enough... hell, even the balance of the bikes when I was holding them up seemed to be almost identical. However, I just felt like the FJR fit me better. The riding position is a little more leaned forward (correctable with bar risers if you want... I don't) and the seat is definitely smaller. Even standing still though, the K felt like a big bike while the FJR felt smaller. I decided I'd prefer the sportier FJR and haven't looked back once.
I will say that at least with the Corbin seat, there's plenty of room and I could flatfoot it a bit more comfortably than the K bike. However I've not felt an FJR with a stock seat in about 3 years so I can't say with any certainty that there's much difference. However, the amount of two-up space does seem to be less than I had on my Concours 14... I can feel my girlfriend behind me while on the Connie I kept having to check to make sure she was still there after a fast takeoff. That's not a bad thing... and she's definitely not up against me in any way.
I'm 5'10", about 180 and she's 5'2" about 110... and there's plenty of power in the FJR to get up and go.
I will say though that either bike will make you deliriously happy in the twisties