I have done a few tests making 16K res terrains.. in all cases Gaea has been able to fit it into my 128 GB of ram.. but when it gets to the "mesher" node in build swarm it immediately crashes build swarm.
I have tried 4193, 5000, 8193 terrain resolutions on a few terrains- all exhibit the behavior above.
I have had consistent success with 8k res and any vert mesh res all the way up to 8193 terrain vert resolution.
** One thing I thought also worth bringing up as a result of my tests is that there were pretty stark differences in the mesh outputs depending on the mesh vert res - and I don't me quality - I thought the camera moved, because shapes had changed so much. I was surprised how much "softer" the 8193 version of the terrain was.. vs.. the same exact terrain, same 8k res.. but at 5000 verts.. which seemed "inflated" not just jaggy.. I would of expected the primary and secondary forms to be pretty stable at these resolutions and only fine details to be the difference.