I played once more with C4 (I have too little time for this fantastic tool) and I can say it is really fantastic. The material editor helps to tweak the material setup to the right point and playing with dynamic lighting in real-time is fantastic and fun.

Besides that it is simply well thought. Lots of stencils will slow A7 down. But in C4 you can mark a light as "static" and it will cache the shadow volume to not render shadow-volumes every frame and thus it is much faster even with lots of lights in a room.

Shadow maps are also available and you can use ambient spaces for control of distribution of light. Future upgrades are announced to have some kind of real-time radiosity within those ambient light spaces.
If you walk inside such an ambient space then your model or weapon will be affected by the shadows in real-time.

Here is a little shot from C4 made with some of my textures and 3 point lights, no shadows, nothing special:




This is a very promising engine and will outperform many others with ease because of very well thought optimizations in scene management (portals and zones) and lighting.