Comparison of Monochrome in post (using a B&W filter in Premiere Pro CS6), or in camera (using a monochrome profile). Also compares MPEG Streamclip and 5DtoRGB. Also compared WB settings in mixed light.
In this scene, using Daylight WB gave slightly lighter results than Tungsten, and also seems to have larger noise 'grain' evident, although I'm not 100% sure the two are related. I think that WBing correctly, and using color filter settings within the picture profile to tune your skintone gradiation will achieve best results.
Compressing to monochrome in camera yields better results than shooting color. There is smoother tonal reproduction and hence less visible noise. I imagine this is because the in camera H.264 bitrate is less stretched when recording one set of luminance values instead of three.
Compressing the files using 5DtoRGB also gives an improvement in final quality over MPEG streamclip.
In the final 400% comparison, you can clearly see that the top two images (5DtoRGB ungraded) display less noise (and with finer 'grain'), than the bottom two (MPEG Streamclip, Faithfull with B&W Filter).
Hope this is useful.