I have to say madno2, you're doing a much better job with this IDL in Poser than anything else I think I've seen so far from anyone.
So congrats on your perseverance!

As for your question "But does it really need to take 4 and a half hours?"
No, not for that. Lightwave 9.6 with a quad core could crank that out in maybe 3-10 minutes. Only with better quality and no splotchiness. Yes, it really is that much faster. You could also get about the same times with Mental Ray in 3ds Max, Maya or Softimage as well.
Firefly simply isn't up to the task. I don't understand why they're even trying it, except maybe because they don't want to spend the money to license or develop something new.

But considering how far you've come so far with dealing with Poser's render deficiencies and still getting something good out of it, I think you'd master a better render engine quickly and be able to get the results you wanted - and then some - far easier and definitely far quicker.