Its a good question, and at the end of the day its gonna vary from person to person.
In the endgame, we are basically forced to get Berald/Eiburns to increase our probability of completing 1370 ghost ship. Failing the event is pretty crushing, so imo Berald is a must.
Instead of spreading resources across sailors for multiple ships, I decided to all-in my coins on the Relic/Legendary Eiburns sailors. Combined with the Hermidas song, this allows me to get resistances up just enough to participate in every endgame sailing co-op.
Most of us are running Hermidas song skin as well for the + resistances and multi boost.
Fast sailing speed is increased more on the Eiburns than on the Estoque, so depending on your RNG the difference there is pretty negligible.
Eiburns has the unique benefit of losing -40 durability every time you boost instead of -20. Basically, this willl allow you to reach the 30% durability speed buff faster than other ships, and maintain it for longer due to it’s huge dead sea/tempest waters resistance.
When most other ships hit the low durability buff zone, they cant really maintain boosting through these two zones for very long. Eiburns don’t care though, and can comfortably remain from 0-30% durability for a long time without having to repair, even in these dangerous waters.
This buff increases base sailing speed and boosted sailing speed by I think around 1.5 - 2 knots, so once that durability buff kicks in you really start ripping.
All in all, the difference is fairly negligible and if you plan to go for the Astray anytime soon, its probably worth it to keep your estoq and save ur mats.
I went all in on ghostie though and I have no regrets. Astray is such a long way away for me anyways I’m happy with getting the full ghost crew.
Hope this helps