My wife uses a Selle Anatomica. http://www.selleanatomica.com/
She has been using it since our 300k qualifier for PBP 2007 when we took it out of the box, put it on the bike and then put the bike in the car to do the ride the following day. We brought along her old seat just in case everything did not go well but she was thrilled with the difference and the extra seat was just added weight. She has never looked back.
She is very happy about not having injured “female parts” after a long ride, and I must say so am I. She STRONGLY recommends the Selle Anatomica.
I also know a female rider from Texas that will not ride anything else but the Selle Anatomica but she is on a single bike. Additionally I have a few male friends that ride them as well with similar, very positive, results.
That said, other riders have had some issues with stretching when they get wet, but my wife did not have any problems on PBP, which, as you may know, was the wettest in over 50 years. Some male riders did have problems, however. By the way, if the “cut outs” are pinching you, you need to adjust the seat with the wrench that they provide with the saddle.
I use a Brooks B-17, but this may be more of a “I have been using this saddle for the last 30 years and it has worked fine, I am stuck in my ways, my butt is used to it…” thing. I must also add that at the end of PBP I had severe saddle issues, she did not, but I think this may be due to a lack of butt cream and being wet for 780 miles rather than seat difference.
If you are having problems at the 40 mile point, you will be in a world of hurt at mile 740 and not looking forward to the last miles of the ride. Not an option for rides like PBP or the 508 where you have to deal with a lot of other problems besides your saddle.
Keep in mind that keeping you butt in good shape is more of a system of saddle, shorts, butt cream/no butt cream, keep it clean, changing shorts, double shorts, etc… The further you go, the closer this becomes to an art form rather than science.
Are you planning on doing the 508 solo or on a team with other tandems?