I don’t have hard numbers, but I can say that from my tests (I’m actually compiling your fork right now) with diffuse tracing and ambient occlusion, the new AO doesn’t appear to be incurring any hits to performance. The visual addition is well worth the sub-millisecond hit, if any, in my opinion. Area lights definitely hit my sad rig hard (rocking a GeForce 750ti), I usually lose ~10-20 FPS.
I’m starting to zero in on magic numbers to get good performance and quality balances, with a main directional light, sky light, and several area lights in a test scene. Fullscreen at 1920x1080, I was getting about 20-30 FPS with higher quality settings. I can imagine that newer GPUs would be getting healthy 60 FPS rates. I plan to cook out a test and pass it on to some peeps to verify that for rigs with better specs, ranging from GeForce 960s to 1070s and I think an AMD GPU somewhere in that pool. Here is a shot from that test scene: