Shading rate 0.01? Come back in 3 years, it might be done rendering. For every pixel it has to render 100. Try a MUCH higher setting like 0.5 a sane minimum is about 0.2 (For fast previews set it to 8!) You could try IBL again, without AO. Set the IBL light(s) so they DO cast shadows (Yes, that will really work.) Put the light sort of in line with the light source in your light probe. That setup can even work if AO is turned on. Don't forget to add a light set for highlights only when you do an IBL scene. If you don't use a highlight light every thing will look flat.