Loading presets/patches of one instrument is fast, you can switch them even during song (I would do this when the instrument doesnt get any data sent in), switching to different bank with different VSTs take something like 1-2 seconds. But you can put 4 different VSTs to one bank. For example I have Drumatic on first channel, Mellotron vst on 2nd and then couple of VA-synths. And if I can change patches to every one of those, I rarely have the need to change banks.
Sadly I've mostly been experimenting with the ones installed + Chipsounds for now so I cant say too much about other plugins. Every VST needs its own wizard file for installing it, havent looked yet on how complicated doing those would be. Overall the performance is pretty good, some pads and chords can cause glitches (pretty hi-freq buzzing sound) if they have lots of delay on them etc. But for more chip-kind of stuff I think the box is pretty good. If you have any particular plugin that is free and is featured on the list of supported ones, I can try it out.
Heres the link:
http://www.smproaudio.com/index.php/en/ … e-database
You can also download their free software there to test out different configs on your computer! Of course it doesnt tell anything about the performance, but gives you good idea about the software, which is the biggest minus for me.