with an outer sit-bone measurement of 155, should I go with the standard or the narrow for my mtb? I suppose I guessed my hips to be quite narrow because I'm pretty thin, but my sitbones must be another matter entirely.

Are the Brooks measurements from the outer edges of the saddle?

...and faced with the prospect of telling H about buying yet another bikey thing, I'm wondering if I should just tinker awhile longer with my current saddle, just trying to tip the nose down a little more or something...