I agree about the 20 mile mark. That's when you know whether the saddle is right for you.
Can you get to a bike shop that has an arseometer? If not and you want to know what a saddle will feel like before you put it on your bike, I was told this by one of the mechanics at Winstanley Bikes in Wigan :
Put the saddle on the stairs in the shop with your feet on the floor and lean forward like you would do on a bike.
I was in
Halfords once and noticed one of those stools on wheels that are used to reach high shelves.
I used that to try sitting on all their different saddles and found one that is perfect for me. It is their own brand but has Salle Royale written underneath. I have this saddle on both my bikes now plus a third one that I take on holiday to use when I hire a bike.