I am finishing last year's bike build. The seatpost was borrowed and needs to go back to its donor (bike). It's a touring bike in Reynolds 853 (at least the seat tube is). 27.2 dia. Looking at how it's set now there is 430mm from the rails to the first bottle carrier bolt. There's about 25mm setback, but I could probably get away with less, as the B17 saddle is getting towards the part of the rails where they flare outwards.
I'd like titanium (or even steel?) because it's the only other material, with steel, that has a fatigue limit. But most titanium posts seem to have aluminium clamps.
Are there any ti posts that have ti clamps?
Does it matter?
And/or what does anybody think of this:http://freshtripe.co.uk/nitto-s84-lugged-seatpost-27-2mm/
(though probably too much setback for me)
Spa have these, which look OK.https://www.spacycles.co.uk/m2b0s84p2814/USE-Sumo-Titanium-Seatpost-long
If your worry is longevity, I won't think about titanium as a "silver bullet", rather the design and quality of the seatpost itself.
I.e. some people would still believe that carbon fiber is made exclusively to crack and injure the rider, and a carbon fiber seatpost with alluminium head ought to be the worst thing ever done. Truth is, a quality one may be incredibly strong: the older Campagnolo Record/Chorus carbon seatposts were very strong indeed, I've seen people breaking frames while trying to remove a seized one of those
So if I was you, I'd stay away from cheap titanium seatposts, just like cheap carbon ones. There's nothing wrong with alluminium saddle clamps, as long as they're done properly: often you will see that saddle clamps are very small and create a pressure point on the saddle's rails.
I.e. if you look at the Thomson saddle clamp, it has a generous area to distribute the stress, and even if using two M5 bolts is pretty good for a lightweight part.
It's a shame that Campagnolo doesn't do their seatposts anymore, one of them is a Centaur with steel shaft that is good looking and solid, and wasn't too expensive back in the day...