Saddle won't vary much unless you are heavy and it has a few years riding on it. But the Butt will adapt to a saddle that fits. However if it is the wrong saddle- you will have butt ache for a long time.

Saying that- I have had saddles that are fine to start off with but 6 months later have gone "Off". This has happened on a couple of Fizic saddles but has not so far occurred with my San Marco "Aero" or the Flite "Gel Max" after 3 years.