It can vary from one photo to the next and some differences may not be obvious until the image is printed. Trial and error may be the best method to employ.
Some other methods of creating a grayscale image from a color image include:
- Convert to LAB mode and extract only the Luminance channel for your black & white. The result is pretty much like grayscale mode.
- Extract one of the RGB or CMYK channels, using one or combining a couple of channels to get the effect you want.
- Instead of removing all the color evenly with desaturation, use the Hue/Saturation controls to desaturate each channel individually for custom effects.
- Create a monotone (with a color other than black) or a duotone for a not-quite color, not-quite black and white effect.