What I've done is to convert to grayscale and adjust levels, then simply send to Fuji or Standard. It comes out quite nicely. I suspect they do the B&W's separately, because I had one sepia-toned picture which was printed as B&W.
There probably won't be a lot of difference. The problem is that the colour papers and chemicals used by colour labs cannot print pure B&W properly, so there's invariably a colour cast. Same happens if you try to print B&W film onto the same papers.