I'm using the Selle San Marco Aspide carbon composite. Same seat I have on the road bike, but the one on the TT bike is the model with the carbon rails, while the others have the Ti or vanox rails.
In hindsight, sticking with Ti or vanox rails might have been a better idea - sometime I wonder how long the carbon rails will last...
It is very comfortable. Does not have cutout but it has some kind of groove so I do not think it causes any pressure at all.
I'll look for a pic to post. They are a bit hard to find now but R&A still has some, and Token makes a saddle which is almost like the SSM and way cheaper.
Good luck finding your favorite!