I've noticed that when v21 first came out; I attempted to run the shaders on high, and didn't get the best FPS considering what my computer can handle
try restarting your computer, I'm running shaders at max at around 60 FPS now
also; if you want light rays, place an invisible brick with fog B (not sure if it works for the rest), the light rays will show up coming through the fog
its recommended you use this very lightly; it brought my graphics card to its knees when inside MotE mansion the first time
EDIT: appears to require a brick planted inbetween its light source and the fog in order to work