I have never had a problem running out of CPU resources using Neutron, although I don’t use it on every track, maybe three or four tracks in a project. Some of the waves plugins I have are much more CPU intensive than neutron (or nectar for that matter, which I also have and use)

As far as Ozone goes I’m on V8 now and I’ve been using it ever since V2. I’m a fan, it’s one of the best and most useful applications ever written IMHO.

But the workflow I’ve used for the last 15 years is to mix first and then master separately, so I use the standalone version of Ozone, never tried to add it to a project.