Just my 10 cents worth.

I had to use Pose-ray and POV-ray when a couple of my P5 scenes refused to be rendered in firefly (too many figures). The results were pretty good BUT there is a bug in P5 material file export (.mtl) [partner file of the wavefront .obj export] that mucks up the texture references for multiple figures. P6 does not have this problem. If you use P5 then you may need to use a python script to do the .mtl file save and you will still probably have to fix some of the material definitions in Pose-ray.

A big plus for some users is that there is a beta multi-threaded version of POV-ray that will shorten the render time on suitable dual processor PCs.

I have not seen any way to get procedural shaders into POV-ray, although I think you can script to get reflection, bump and transparency maps across with a little tweaking.

Pose-ray is an excellent tool (very easy to use) and well worth a look.