Actually I watched the CPU performance while rendering. Utilisation of all 8 CPU threads was full at all times. 

 

I have found P8 to run very good and fast on my system (in fact so did Poser 7 earlier) and have done so for years.

It is not wise to make performance judgements comparing rendering times between Poser 8 and Poser Pro 2010 - their rendering times are surely not the same no matter what the underlying operating system.