Ah, okay... that makes sense, BB... thanks.

So, does this suggest that (what I'm guessing are) the ray tracing related stages of the rendering process are currently somehow still single threaded... at least in part?

This seems unlikely doesn't it? Surely ray tracing by its very nature is one of the ideal applications for scaling up to / exploiting a multithreading and multicore system?

So, should the process be multithreaded, but for some reason... due to my settings perhaps, or a system resource limitation elsewhere, they're not able to be multithreaded???

Unless OS X is throttling it for some reason I guess... that might be the other explanation.

But, if I compare rendering with Vue... the render engine there consistently uses anything up to just short of the full 100% of total CPU, if that's available to it (no other apps running).

EDIT: But so too does Firefly, apparently... use the full percentage... when rendering a smaller scene... making me go back to suspecting a related resource limitation, e.g. memory...