Well, Doom 3 worked well with my 800MHz CPU and relied heavily on stencil shadows. I am pretty sure that it can still be optimized a lot. It is just well posible that my current approach while being very easy, is most probably also the slowest one wink.

Lite-C Tut. 1 Lite-C Tut. 2 Lite-C Tut. 3 (en)
Shader Tutorial (ger)

http://www.slindev.com