It seems to scale somewhat, not regular, for lack of a better way to describe it. If I back my camera off, where there's less "scene" in the picture, the difference in render times becomes lesser. I guess that makes sense.
And it seems to depend on scene size. Large complex scenes show a greater difference, while a scene with only one figure in it and nothing else will be just about the same speed. I guess that makes sense, too.
So I guess the thing to do is to just take it as it comes, and adjust depending on the scene variables.

I've actually become quite impressed with Poser Pro overall - I definitely think it's the best version yet.
But I think I'll be ordering Poser 8 later this week anyway. In spite of all the problems I've read, the reported increased CPU usage efficiency is drawing me in.