
heres a comparison:
Normal "3D Textured" mode:
"3D Lighting Preview" mode:
(render time: 1 second, only needs to be rendered once every map load.)
"3D Ray-traced Preview" mode:
(render time: ~1 minute, needs to get re-rendered every time you move the camera.)
I have a AMD Athlon64 X2 6000+ cpu and 2 gb ram, so you can guess how long it will take to render on slower pcs.