Quote - Do you find the progressive render options use a fair amount more resources?

It will use less memory, but in most cases more time/CPU. It's doing everything by brute force ray tracing, so there is no irradiance or occlusion cache, no dicing into micropolygon grids, no shadow maps, etc. Hence there are no options for those features, as they're not needed. IDL is calculated with naive path tracing, so the quality of IDL depends directly on the number of primary rays (= pixel samples * pixel samples).