I too have a Harley, 08 FLHT, but also a K100RS se. I love them both, each has a different ride. Go for the K bike, it is totally different from your Harley. I ride one on one day, the other the next.
Seat height will be an issue, K bikes, BMW in general are way higher than Harleys. But you will love the Birck for different reasons.
Bob