Can anyone tell me the difference between these two models? Is the endurance saddle designed for longer rides?
What would you recomend for 4-9 h rides?
Thanks.

What would I recommend for 4-9 hr rides?

Not to be married!
CP

And not have babies I must add

I ride endurance and the last place I try to save weight is the seat. Find something you like that offers different ride positions (for me - wide back narrow long front.) Get a carbon or Ti seatpost to dampen the road chatter

I used Selle italia SLR last season and it was ok, then I stopped riding for 5 months and now It doesn't feel as comfortable as last year, in fact in hurts...Im sure it has deformed or something like that...

check you have not bent a rail. You can pull a glute muscle or the head of your Hamstring over time from something as simple as that

Yes, the Endurance was designed with the focus on long rides.
In general the Endurance is meant for large men and also for women, while the Sprint is for small - normal people.

I've never ridden any, but many riders with AX-Lightness saddles say that they're on par or even more comfy than a classic Flite.
I guess that's also the reason why many Pro roadies prefer them over the saddles from their Team sponsor.

Unfortunately there is probably no way to know for sure until you try them out, but you can compare the dimensions to other saddles you like and eliminate some from contention that way.

I am not at all a large person but like the Endurance better. I think because I ride with my pelvis tipped way forward the slight groove at the rear of the Endurance keeps the pressure off better and Mr. PeePee no get sleepy even on 6-8 hour rides. I never could get that comfortable on an SLR because it bumped up at almost the same place.