I can't answer your question - no doubt it depends on the faceting pattern and the angles. You would have to check the actual stone.
But I'm interested in what you are planning to do with a pentagon stone. I ask because I have a tourmaline pentagon that I bought because it looked cool, but I'm a bit puzzled at how to set it.
I was thinking of having a piece made with a pentagon cut as the central stone. I haven't found many good images of this cut.
Any expert or enthusiast's opinion (or images) of how this cut performs?