Very sorry aRtBee... I wasn't meaning to come across like I was being dismissive of your advice... in case I was?? Many apologies if so...

I see your point re. 25% being more like equivalent to two threads on a quad core (or I guess one core)?

Anyway, as I said, I've realised what I'm seeing definitely only seems to kick in after the scene gets beyond some sort of complexity... what I think ssgbryan had suggested to me back at that Rdna thread I started previously on this was that it could be memory to CPU ratio related.

In that Rdna thread I been talking in terms of Queue Manager... but I guess QM or Poser background process... both are managing Firefly... and its the FFRender process I'm essentially talking about here.

So, what I wasn't making clear at the outset, of raising this point, was that there seems to be this aspect to the issue... of scene complexity...

...as I said, I'd need to investigate more myself to see if I can identify the point (in terms of scene complexity) at which IDL and final passes seem to stop utilising much more than 25%... on my system at least.

So I really shouldn't have probably brought this up in this thread... sorry!

Cheers ;-)