Scan in 16 bit RGB, then look at each channel's noise independantly, pick the lowest noise channel(normally green or blue) remove the other two, and make your desired adjustments from there.
Don't just desaturate as it will give you the worst possible conversion.
Color negs and transparencies are better scanned as RGB, then converted to b&w in Photoshop. This will give you a *lot* more control over image contrast and how tones are rendered. Just desaturating will usually not provide the best result. There are a lot of strategies for converting -- this is a whole other
topic
I scan b&w negatives as 16-bit grayscale. Photoshop tells me that all the channels of b&w negs scanned as 48-bit RGB have identical histograms, so I don't think there is anything to be gained (except file size) by scanning these as RGB.
For C41 process or real B&W films there's no need to scan in RGB, except for negatives developed in staining developers; you'll usually get better results by scanning those in RGB and choose which channel(s) hold the most useful data (=broader histogram + less noise/grain) later in PS...
for black and white film, scan in 16 bit greyscale or if you wish 48 bit colour and then discard red and blue channel (it is the same thing if you try it).
I also recommend you scan in postive mode as you can adjust the black and white points easier and not have a funny gamma associated with your scan by the epson driver. You can then apply any curves as you desire later.
I scan b&w negatives as 16-bit grayscale. Photoshop tells me that all the channels of b&w negs scanned as 48-bit RGB have identical histograms, so I don't think there is anything to be gained (except file size) by scanning these as RGB.
I'd like to know how scanner noise behaves if you compare an RGB scan (converted to B&W afterwards) with a gray scale scan (straight from the scanner). With an RGB scan you basically take three samples of every pixel, which, if you average them, should reduce noise by a factor of 1.73. This may, of course, be a moot point, if the scanner internally does grey scale scans like this anyway.
I scan b&w negatives as 16-bit grayscale. Photoshop tells me that all the channels of b&w negs scanned as 48-bit RGB have identical histograms, so I don't think there is anything to be gained (except file size) by scanning these as RGB.