I binned the San Marco after 1 ride and fitted a Brooks B17.
It's the best, no question about it in my opinion and zero breaking-in time for me.
Check out the pictures on
http://www.pbase.com/canyonlands/fullyloaded, considering the number of different saddles available it's no coincidence that a high proportion of high-mileage riders choose Brooks.
Mine has never sagged into my shape (maybe I'm Brooks shaped) but is comfy anyway.
I have spent 16 hours a day on it on some occasions, I doubt if I could stand San Marco for 2 hours.
Also, because the leather is suspended (like a hard hammock) between nose and tail with nothing else in-between it acts like a suspension seat-post. If I push hard with my hand on the top of the saddle I can see the leather depress by about a centimetre.
Anyway, they've been selling them over 100 years without much in the way of modification. They must be doing something right.