Poser doesn't use multithreading or dual processors. So it won't speed up your renders.

However, many people report it's more stable with dual processors, if you're the type who likes to multi-task. You can use your computer for other things while Poser's rendering if you have two processors.

This seems less of an issue with P6. P6 is much less likely to crash if you're using your computer for other things while rendering, at least IME.