Or do I need to Freeze that track?  I can't tell looking at the Performance Meter.  Also couldn't find answer with search through the reference manual.

Yes, 'Bypassing' plugins (or entire FX racks/bins) frees up CPU. You can see this clearly by clicking the 'FX' button in the Mix module to Bypass All plugins which will make the change in the Performance module more obvious.

Ooooo.  I wondered what that FX button did.  Now I know.  Silly me.

turning off the FX button can also be helpful if you are experiencing timing issues in Melodyne (but turn it off before opening up a clip in Melodyne region fx view)

I regularly hit the E button when I start overdubbing and back again for listening/mixing.
 
Brings the latency right down

Bristol_Jonesey
I regularly hit the E button when I start overdubbing and back again for listening/mixing.

There are good and there are sensationally awful times to discover the "e" key. Before I had any idea of it's binding to bypass all FX and EQ I accidentally pressed it at the start of a song during a live gig. 
 
As a result, on my gig laptop the "e" key is no longer bound:)

I now routinely record the synth audio at the same time as midi...This is fantastic!  Quick and easy to split into clips and get a rough song idea.  However many of my Omnisphere multis are cpu hogs... and just muting the track doesn't seem to free up cpu... so,  how do I disable the synth to free up cpu without deleting it?  I want to be able to reenable it to do editing of the midi down the road
 
Thanks,  gurus!

If you are not going to archive or freeze the synth:
If the synth rack is docked, select the synth in the synth rack and use the menu in the synth tab to disconnect the synth. Otherwise use the power button to the left of the synth icon for the synth in the rack to disconnect it.

Thanks, scook as always!  now I see it in the synth tab...  but what do you mean by the "power button" next to the synth icon"?
 

Undock the browser. The synth rack will widen and show much more including a power button for each synth.