Kieran,
I would say the C17 carved is noticeably less flexible, owing to the shorter slot. The SA Titanico X felt good to me in the first few miles, but I would develop the same problem as the C17, where it feels like the saddle is migrating into soft tissue because it's too narrow. Also possible that I'm sitting on rather than between the frame structure. Hardness isn't so much a concern for me, as I rode comfortably for years on a very hard and unslotted Berthoud saddle. I think it's more matching up the body-saddle geometries for me, but I like the flex and possible pressure relief of a slot.
I need to take some long rides and see how the C19 fares in this regard, but I think it's going to be much improved based on the absence of discomfort on short rides. Assuming there's no pain/numbness on long rides, I think the C19 might be the perfect saddle for me with an SA-style slot. I've also contacted Rivet to see if they'll do this, since I haven't heard back from SA. I learned a lot about saddle fit just by reading the Rivet site!