What about a Selle San Marco Glamour Aspide? Very firm, 155 mm wide across the back, with a depression but no cutout. I'm not sure what the width of an Arione is. Ultimately, the lack of a cutout is what led me to give up on it. I can ride cutout-free until about 40 miles, and then I really need a little extra space there.

Or what about a Vitesse? I believe that's Fizik's womens model.