sharpening and noise reduction,before or after b&w conversion ?

Hello,

I was wondering if it made any difference or if there is a so called ideal workflow for doing image sharpening and noise reduction when converting from color to b&w.I ask the question because most often the converted b&w requires tweaks to clarity,contrast etc for a well balanced image,even if the color file has already received full processing including sharpening and NR.

Thanks