The Selle SMP line probably does have the largest cutout around (although there is the ?Arione? that someone pointed in another thread with a nice cutout). But the Koobi and Selle SMP are very different saddles with very different shapes. The Selle SMP Lady Strike is wider in the back than any of the Koobis.

Except for its cutout (which looks very interesting to me, but, alas the rear is too narrow for me...sigh), the Koobi is a more traditionally shaped saddle. That is, relatively flat nose to tip and side to side. All saddles vary in their curvatures, but the Selle SMP really stretches the limits of curvature rear to nose.