casek,
In 1997 my dealer had a '95 Honda Pacific Coast and a '95 Kawasaki Concours on the floor. Both were used, about 6000 miles on each, and both looked to be in great condition, price was about the same. I joined Yahoo forums for both, asked questions, and read what test reports I could find online. I went to the dealer a couple times and sat on both bikes. I became 90% sure that the PC was the machine for me. The snow finally melted (it was February in Connecticut). I bundled up and went to the dealership. He rolled both machines out, tossed me the keys, and said "have fun". (I had done business with these guys for years.)
I rode the PC first for about 30 minutes. Interstate, back roads - a good variety. It was darn cold out, and my 6'6" self wasn't getting very good protection from the PC fairing. Performance seemed to be very "car like" - acceleration wasn't all that exciting. I then rode the Concours over the same route. Fairing protection was much better for me (it did have a Rifle aftermarket windscreen). And it leaped eagerly when I twisted the throttle - much more exciting performance. I went back to the dealership and bought the Concours. The test ride simply blew away all of the logic I had assembled over the past several weeks... I made the right decision at the time - I owned that Concours for 6 years and 60,000 miles (longest I've every kept a motorcycle).
It would be interesting to have someone who rides a Burgman 650 test ride a good used PC. My guess is, that despite the 800cc engine in the PC, the Burgman 650 will feel sportier. The PC would have an advantage in ride quality (bigger wheels & better suspension) and probably in performance from 95 mph on up.
I hope you locate one & can ride it. It would be interesting to see if my guess is anywhere close to the impression you get.