Saddle preference is so personal…what works for one person is a torture device for another. I winced in pain when I saw you rode an Arione for years on a tri bike.
I used the Profile Stryke saddle for many years and had great success with it…but I would not recommend it to anyone. It is the exact opposite of what most people recommend for a tri saddle…it is very big and has an extended nose. But for whatever reason, I got on well with it and could get very low (see profile pic)
I currently have a Specialized Sitero. Overall, I like the shape and how I sit on it…but it is a pretty firm saddle and I wish it was a bit softer in the nose area. Dunno if I could do a full IM on it or not.
Lots of people like ISM saddles, but I never found one that was comfortable.
Cobb saddles can be worth looking at as well.
Your best bet is to find a retailer, fitter or supplier that has a trial program. CObb used to have a 30 day return program, but I don’t know if that still exists. Specialized has a saddle trial program through some dealers.
It is very much a trial and error process…unfortunatley.