Is it a sacrifice comfort for weight savings issue? Does it not really make much difference to have that thin piece of pad & leather there. In other words... would I notice much difference going from a SLR saddle to an SLR full carbon saddle?

I have an SLR Evolution (carbon shell, no padding, Ti rails). I like it well enough, but not as comfy overall as my SLR XP. With a decent chamois it's not bad, although sometimes the nose catches on my shorts as I sit back down from climbing.

If you want it, PM me, as I think I'm moving back to an SLR XP.

Depends a lot on your riding style and how well the saddle matches your anatomy. If you hammer hard all the time, you will have much fewer saddle problems than a less athletic cyclist.

One full carbon saddle...I tried the Selle SMP Strike Carbon at Interbike and found it to be comfortable, but the real test of course is using it long term. I think with something as hard as a full carbon saddle, you may need to put more emphasis on making sure it doesn't cut off any circulation (as stated earlier, anatomic compatibility), and has a design that's friendly to you.

I tried a Sella Italia some years ago and had to put one of those Quintana Roo Mr. Flite neoprene covers on it to make it comfortable for more than a short ride on smooth roads.

A buddy of mine uses a carbon hardshell for climbing races like Mt Washington, where you're out of the saddle for half the time anyway. It's a nice bit of bling if you can afford it, but he doesn't ride it every day (for a reason).

Now if you were riding an Arione K:1 it would be a different story

I've had three other saddles and I like my carbon saddle the most, by far. The feeling is, you're obviously sitting on a piece of plastic, but I never get pain when riding it like I did with my other saddles. I'm 150 lbs so that may have something to do with me liking the carbon saddle so much.