Jaquisun - take a look at www.wallbike.com That site sells Brooks, and I freely admit to being a member of the Brooks cult. But at least they have the length and width measurements of all their saddles!
My center-to-center measurements are already very wide. For choosing a saddle I will use my outer-edge to outer-edge measurement, because I'm not comfortable unless my entire bone is on the seat and has a little margin of error. (center to center I'm around 170-180 mm, outer to outer I'm around 200 mm)