From my understanding (limited as it may be), CIE is best for scenes with no direct sunlight (overcast sky), while Perez all-weather is best for clear skies. I'm not terribly familiar with daylight simulations, but here is a source that may help clear it up (or at least be more informative than I) - particularly number 3. It seems to be a lack in clarification by the USGBC in their requirements and SOP in daylight simulations.