A* Pathfinding or NavMesh

I don't have a lot of experience with Unity's navmesh system, but I have been using Astar pathfinding in my own project for the past year or so and this is my experience with it:

My project uses some very large terrains, usually around 30x30 kilometers. I have been able to use Astar pretty much out of the box to make the navmesh for these scenes with a couple caveats:
1. You need Astar Pathfinding Pro version to use the recast graph
2. I had to bake the whole terrain into one navmesh. I tried for a very long time and was unsuccessful at stitching together multiple smaller graphs. For a scene of my size, the graph ended up being several gigabytes.
3. My scene is static therefore I didn't have to worry about baking the graph at runtime
4. My graph had to be fairly imprecise in order to accomplish the bake
5. My terrain is not streamed.

I do know that it is possible to do procedurally generated / streamed worlds with Astar, and this involves creating a very large graph that covers the whole theoretical area of the terrain, then asynchronously telling specific tiles in the graph to bake as the terrain is streamed in. I do not, however, know how well this works or what the limitations of it are. I do have to say that I doubt that Unity's system accomplishes this any better though. Astar is also open-source, so if you need to mess with source code to get it to work then you can. Either way I expect you will run into some hurdles.

Unfortunately I don't really know the "right" way to tackle a problem like this within Unity