AcousticSamples has posted a new version of B-5 that is a bit easier on the CPU. The file is dated in late June.
I have been tracking organ parts at home in Cubase and rehearsing/performing with B-5 over the last few weeks, and it sounds/feels fantastic! I have been controlling it with both a Hamichord M-C3 and a Numa Organ 2. The preset MIDI maps for these controllers do require a bit of tweaking, but they are an excellent starting point. All of my presets use the C3 model that everyone seems to prefer, coupled with the 122B Leslie model on High quality.