Hi there,
the second riddle (as referred to in here) is subdivs for reflection glossiness and light samples: with those variables gone, is it only possible to control image smoothness, globally? edit: through Raytrace --> Quality --> Noise Limit
Denoiser is OK… so long as you do a reasonably high-quality render first and set the denoise level to ‘mild’. It fucks with things behind glass a bit, same with reflections and results is loss of detail sometimes… so it’s not the most reliable method
To negate loss of detail in certain parts of the render output you might want to try masking the Denoiser channel result in an image-processing software of your choice and using parts of the RGB channel wherever needed.
Overall, the pros of the Denoiser channel vastly overweight the cons.
I know, it’s an old post, but did you got problems if you use output gamma 1? If yes, than jump to output gamma 2.2 and disabled sRGB at the frame buffer. Helped here a lot against noise at dark areas today.