I read an article that was posted on this site somewhere about saddle fit...and the basic rule was that your saddle should be at least as wide as the middle of your sit bones.

So if your middle to middle distance was 158mm your saddle needs to be at least this wide to properly support you. The reason for this is that if your saddle fits in between your sit bones, all the pressure will be on your soft tissue and pelvis and after extended periods of sitting, it could cut blood flow to important areas (there are key arteries and nerves running along our thighs between the sit bones).

I have the reverse problem...my sit bones measure narrower than 140mm and most of the 'women's specific' saddles are way too wide for me (my legs rub too much).

Another point of note: 158mm = approximately 6 1/4 inches. I believe that there are quite a few ladies Terry saddles that make this measurement.