I have finally gotten round to properly measuring my sitbones using the playdoh method. I've come up with:
Outer: ~160mm--I couldn't get a clean set of butt-prints for the outer edges
Center-to-center: 130mm (between the centers of each marble)
Inner: 75-80mm
Other criteria:
Shape: Currently using a SI Lady Gel Flow, which is rather too pear-shaped for my liking. Need a T-shaped saddle.
Padding: Not too much padding, obviously, but I need some.
Cutout: Necessary.

TE ladies, work your magic! I've got the old Jett on my list (I believe the LBS still has one of each in stock), not sure about the new one.