If you go to the Terry site, and click into their saddles, dimensions are given for all of their saddles. You probably want one of the saddles that is not as wide in the back. The Butterfly Tri is 6.1", therefore you want smaller than that. The Damselfly is 5.1", the Firefly is 5.5" and the Liberator Race/Gel is 5.8". All of their saddles have the cut-out.

http://www.terrybicycles.com/saddles/product.html?t=w


Darcy