A lot depends on your NEEDS...
......... I want a GREAT arranger, but I also want a GREAT WS too. And I would prefer them both to be the same piece of gear..!
Kronos with a PA arranger engine...now THAT would be just about nirvana!!!
Even then most people are still not satisfied.
And what does the BK 5 have that the PA500 don't have? Seems to me that the BK5 don't have alot of things the Korg PA500 have for example pads and a decent sequencer.