Path tracing uses a lot of rays per pixel. I do a single eye-ray and a few to the light sources for the surface intersected, and of course reflections. I do have a scheme for handling large numbers of light sources to some extent. I would say moderate complexity definitely includes a near-full-screen object of arbitrary polygon count. It may also include environments like anything from the quake series - including light sources. Of course I need to buy one of these things and try out the old code to see if we're really there yet. Until then I'm still speculating.