I am using pbrt with Visual Studio 2003. At first I installed it in a directory where the path consisted of spaces and that didn't work. Otherwise, installation went mostly smoothly.
When adjusting the paramters, I rendered my images at a resolution of 150x150 with number of pixel samples equals to 2. The first three configuations took less than 10s to render. For the fourth configuration, I tested the lights individually, so speed wasn't a problem.
I was mostly playing with the transformations. Defining the area light location in the camera coordinate system was a little confusing in the beginning because I didn't know where the light initially was and where it was pointing.