This is an idea taken from the jBridge utility http://jstuff.wordpress.com/jbridge/ (my idea originally, in fact
)jBridge has a performance mode option that adds an additional buffer of delay to a single VST's audio i/o.
In Usine 4.2, I can achieve a much higher VSTI count at lower cpu without crackling if I use jBridge and enable performance mode for each plugin.
While this does not always make sense for VST FX as there is added latency of one buffer for each plugin that would add up in series, it makes perfect sense for VST Instruments where it can be easy to live with or compensate for a tiny bit of latency.
With a soundcard buffer of 128, the combination of midi to and audio from a VSTI is delayed about 1.7ms and I can run apprx 40% more instances of the VSTI than I could internally in Usine 4.2, and on my current setup is actually more effective than increasing Usine's bloc size.
If at all applicable to how Usine works internally, this might be a great option to be able to select per plugin.