The latency issues are only present when too many samples are loaded into a multi. For example, I have Collossus and Kontakt II,(to name just two), which have some pretty hefty samples. You can load 8 large patches into a multi, and it would drag down the cpu if all of them were on at once. Even with these huge samples, if you mute a few of them, you are fine. BTW I am talking about samples. Normal VST's present no problems. Another tool is "Snapshots", which does as it implies. You bring up just the patches you need without loading time.
I played my band gig yesterday, using B4II, which is far better than any arranger. I got all kinds of compliments. The program is about $259, and the best B3 emulation out there( in many peoples opinion).
With your inquiring mind, you would love it, although it is deep, but well documented, and the Receptor forum is great. Muse owns KVR.
pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact