Unfortunately picture.datatype in OS3.9 is just much slower than the 3.1 version, no matter what bitdepth the images being used are. I have pre-remapped every image I use in all of my programs to a special, locked 16 colour palette. In a program like YAM, which needs to load many of these images on startup, the difference in load times between 3.1 and 3.9 is very noticable. It takes less than a minute to load in 3.1, but over a minute to load in 3.9, and all the images it's loading are 4bit 16 colour iffs.