I think that it's good that you haven't posted a comparison shot, because 99 times out of 100 I wouldn't choose selective colour as my favourite. You also chose a very difficult subject to try to salvage all the colour tones from. Having said that, this one seems a bit different than normal because there's still a little colour in the background instead of being completely b&w.
I understand that using selective colour needs to be done carefully and I wanted to make the sax stand out rather than merge into the background, I also feel the tone of the sax compliments the sepia tone of the image quite well and serves as a stronger element rather than a contrasting colour.
There's a time and place for everything and this is certainly a great example of when selective colour has been used to best advantage. Nicely done!
Gosh, Ian .. you're so giddy with your new X100 that I see it has given occasion for you to start a new blog .. 571 Photography. I like it .. the simple black page style does wonders to showcase your images.