One that is comfy enough for multiple days riding of 15+ hours duration is my own personal conclusion.
Unfortunately, the only real way of finding that out is by doing it… 😜
You don’t need anything fancy, if you’re bagged up that all kind of limit the likely terrain so geo isn’t really that important either.
I started on what I had at the time (a mk1 Solaris). I ‘graduated’ to a mk1 SolarisMAX built up from new for the sole purpose of bikepacking (B+, boost, 2×11, fixed seatpin, barend ergon grips, comfy saddle (this took a couple of goes to get right…)). It’s done many trips and done the job.
I’ve ‘packed on the Sherpa too (just not multiple long days), it was fine. It would give you wheel options.
I’m about to swap the mk1 SolarisMAX for a mk2 (my original dark metal in fact) which my mate has used for multiday trips without issue (solo and with myself). So I’m sure it would also be up to the job.
However, if you go to bikepacking.com and look up their readers rigs (or whatever they call it) and you’ll see it doesn’t really matter…
I’ve been away, I need to check in the loft (tomorrow) before I reply to the pm… 🙂
ETA: bags wear paint so Ti is nice. But tape is cheaper… make sure you buy plenty of decent stuff and cover the main triangle and especially the head tube.
Re-reading your OP I’m planning on riding the Camino del Norte next year. I’ll be doing it on my standard ‘packer but with reasonable rolling tyres on 29er wheels as a compromise.