Odd there is a problem with just four figures.

You mentioned problems with Poser becoming laggy even before V4/M4 are added (first post), could the slow response with the new scene be related to that issue?

When Poser is performing badly have you looked at the CPU, memory utilization and disk performance to see if they are much higher than expected (ie near 100%)?

I've never used a Mac so don't know the correct name, but are there system and application logs, do they show an increase in error messages when Poser starts to slow down? Is there an error message associated with the Poser crash you mentioned in the first post?

A grasping at straws type question in case its an OpenGL problem - if availabled on the Mac have you tried changing to the preview render engine to Sreed?