Excellent work! This looks wonderful.
There was one other thing: Daniel Wright told me that the lumen team used a tonemapping trick with lumen reflections when they needed them to work irregardless of noise: r.Lumen.Reflections.ScreenSpaceReconstruction.TonemapStrength 1
AFAIK it looks at high-energy regions of reflections and clamps them, so it erases noise but also a lot of fine reflection detail. If your lighting is pretty broad and strong, you won’t lose too much however. It’s currently just an on/off, but in 5.4 they’re making it adjustable, so you can tune your signal/noise ratio according to what’s acceptable for your level.