I think they are both good bikes for the task. I've only ridden the GS650 but I did own a GPZ500 for a while and the engine is awesome (shared with the KLE albeit in a higher state of tune in the GPZ). Gas mileage and comfort is likely to be slightly better on the BMW and you can tailor it with a greater selection of OEM & after market farkles.
One definate advantage that the BMW will have is the quality of finish. I'm not saying the BMW is more robust than a Triumph/Honda/Harley etc. but every Kawasaki I have owned has had a distinctly delicate feel to the finish. The exception to this is the engine paint which is likely to be better on the KLE.
I delivered my mate's GS650 to him in Ireland early this year (in snow). Went 2-up, cruised easily at 85mph and was well impressed. Owners of earlier model KLEs have also praised their bikes so it's worth getting a test ride if you can.