I stumbled across this thread over in the DAZ forums [ https://www.daz3d.com/forums/discussion/316206/denoise-renders-and-save-a-lot-of-time-nvidia-not-reqd/p1 ]
I had to try it out. This image was rendered at 3840X2160 @ 10 Iray iterations (1 min render time). Then I ran it through denoiser.exe (4 sec), The results blew my mind.
Here is another test rendered at 4300X1950 @ 10 Iray iterations (1 min render time)
Of course, these would be better with longer render times :)