First, the riding position, although feeling strange at first, turned out to be more comfortable than the more upright position of the RT. Second, the 1330 engine has more lower-end torque and was faster but not unmanageable.
Third, the styling of the bike is sportier. Now, I am actually a slowpoke, but on the F-3 I felt like I was moving faster than I was.
It's not realistic for me to actually trade in my RT after such a short time, but since I bought with the intention of ryding with my wife who turned out to be very reluctant, if I could go back in time I think I would have chosen the F-3 instead of the RT.