Any audio channel track or VSTi track that has the I/O-helper plugin inserted in it will run on the processor which currently is mostly unused. This means you can get some extra power out of the processor which formerly only ran OS and MIDI/screen redraws etc.

To do this , just do the following:
Insert the I/O helper plugin in any Audio object (Track or Instrument, etc).
Set the Output in that plugin to be any available output (don't leave it at "--" which is the default - you won't get the benefit if you don't pick an available output).
Option-click the insert to disable it.
Any plugins on that channel (including VSTi's) will now use the much less heavily loaded processor.