I once had a B17 Narrow on which I did many thousands of miles, it took a long time to break in but after that is was fantastic. Unfortunately I was seduced by a Swift with Titanium rails and I let the B17N go with my Galaxy to a new owner.
The Swift Titanium didn't suit me, somehow I felt I always seemed to end up sitting on the rivets.
I have tried a few B17 Titaniums, but I have the same issues as Dan. I don't want to end up with the hammock shape, and it seems to me the B17s are getting softer/thinner - perhaps to make them easier out of the box I wonder?
...I much prefer the harder ones, as they remain dome-shaped a bit longer. I've several that are just barely broken in that I need to sell, as they are no longer my preferred shape and are a bit too soft for me.
Also, my B17 Titanium recently had some sort of mishap and ended up slightly wonky...
I am now trying out a B17 Select on my RST, hopefully it will retain its shape longer ...
P.S. I am also trying out a Team Pro Titanium on my Audax (again) which will need a lot of breaking in, but if it ends up like the B17N then I will be delighted.