The 9kpro has modeled organ flutes that are an improvement over the psr series. (even the 9000), and I do believe that it's MORE than close - it's damn good. I do admit there is an advantage to the B4, but not a huge one. If you are already bringing a computer to the gig - then go for it, if not...it may not be the best solution for you. For one - the outputs on MY laptop are kind of noisy. Now, that's ok for an organ sound, but in the rests... it still comes trough.
I love the tone of the B4, I do - but the 9kpro is awesome too.
As to the GEM ....... I better not. I have a low tolerance for their sound - even their high end stuff. My choice - not for everyone.