There is an interesting PDF of the IRAY by NVDIA here:  http://www.nvidia-arc.com/fileadmin/user_upload/iray_2013/documents/iray_whitepaper.121206.pdf

It will not help with specific rendering questions, but it is nice background information on the process.  What's also interesting is it allows for the actual rendering to be done on another machine while you continue working, including sending it to cloud based servers.