Interesting....I use Pro Tools. I recorded a pass using an instrument track with one instance of Omnisphere and another with Stylus RMX running a simple single pattern. I recorded each of these to an audio track and then removed each instance of Omnisphere and Stylus.
So now in effect all I had was 2 audio tracks with no plug in's and two MIDI tracks. The whole thing was less than 2 minutes long.
Anyway, I went to add another instrument track with Omnisphere on it and got the error message that I was running out of CPU power!
I promptly opened my System Useage window in Pro Tools and it hardly even showed any load at all.