Yeah, the problem with too many HDRi's is disk space.  Those files can get pretty large depending on the resolution of the image.  Going over 5k for Poser is overkill IMHO.  You can easily cripple the software that way.  I am currently reading The HDRI Handbook 2.0 by Christian Bloch, although it's a bit dated, it does give some handy insight into dynamic range images and how to work with them.  I only have the digital version, the hardcopy with work disc is way, way overpriced.