We're currently running a single protools session for a film mix and we have ProQ-3 running on about 320 tracks. (Auxes and audio tracks)
We stumbled across an interesting side effect of using natural phase vs zero latency vs linear phase modes:
We will often group large amounts of these tracks and change their presets at once in automation preview mode, then write that to a selection in the tracks.
What we noticed is that when clicking around (i.e. when moving the playback head from one spot to another thereby triggering protools to read automation on the tracks), if a lot of ProQs have to switch presets at the same time there can be a very nasty 'CPU spike' (by looking at the system usage window in PT). What's more important is sometimes this spike is enough to freeze protools entirely, or cause playback issues and force us to restart protools.
We then started to mess with the phase modes and learned the following:
Zero Latency mode: Cpu spikes to about 50%
Linear Phase Mode: Cpu spikes to about 60%
Natural Phase Mode: Cpu spikes to 100% and cannot recover always
All this to say, it seems that Natural Phase mode uses up too much cpu to use reliably?
I'd be happy to provide a PT session so you can see for yourself.