What Software works best?
How best to accomplish clean ISO 1600 & 3200 Images?
I think you might be asking about film used in less than optimum lighting condition where you can’t use flash.
Today programs like Noise Ninja and Topaz Denoise and the App in the now DXO Lightroom and PS plug in “Nik“All give great noise reduction.
But with B&W film, getting just a snippet of the first few frames processed first by a lab devoted to B&W film will allow control of processing and the best possible grain structure to your liking.
Then the processed film needs to be optimally scanned!
All that before we even consider grain and noise!
Asher