Sky Models

   3DS Max presents us with 3 different sky models to use: CIE, Haze, and Perez. Note that all the images below have undergone levels correction as a post process.
   At render time, the fastest was CIE, then Haze and Finally Perez. Apparently CIE is designed to be fast and accurate, and Perez is designed to be used in conjunction with real weather data files. It appears to me as if the haze driven model is designed to look accurate, without actually being so.

CIE System

Haze Driven

Perez Model