Well nadro just a small correction to your idea.. you dont need a pass per 6 lights, you can do them all in one pass but you have to do some workarounds.. I did 68 lights Deffered Shading in just 2 passes (because irrlicht has options and functions like GLSL you can call them but they dont do anything, I mean the availibillity of 8 textures per material, I had 5 and irrlicht only passes 4 to a shader, if I had 8 max textures then I could do it all in one pass.
http://www.youtube.com/watch?v=3-r88vbo-LE
EDIT: I know the topic is dead but,
I get 300FPS on deffered shading in low poly mode
150 FPS in forward
50 to 60 in deffered high poly
1-14 in forward rendering
this would cause to say lets go deffered on 8800GT and above because its faster than forward even with 4000 poly. but the thing is that nadro drew the geometry each time he did a pass for the light in ForwardRendering... if i am correct.