Are large RGB maps (as opposed to procedural textures) advisable for terrain textures?

Below, I show a RAW height map from USGS as a Unity terrain -- the top image is a (very small) tile of this input map shown in the hillshade view below.

Since this terrain matches a real world place, I'd like to use available satellite photos as the RGB texture; the second image below is a 3D view where the terrain is textured with a photo.

I realize that this approach may well quickly get too heavy for Unity. The Unity documentation suggests using procedural maps (https://docs.unity3d.com/Manual/terrain-Textures.html), which naturally don't carry the overhead of individual maps.

I'm aware of several terrain editing packages (World Builder, Real World Terrain, et cetera) that take a similar approach: they prefer to build up a layers of procedural textures rather than rely on large high-resolution textures.

Of course, there are two main problems with the procedural texture approach for terrains:

• Specific photographic details of the place are lost in a procedural approach: in my example below showing satellite photos, the shore line, structures, vegetation are all quite specific to this place. Making hand-mapped layers of different algorithmic textures would lose a lot of the reality of the place, especially is the viewer can get as close to the terrain as in my examples.

• Not only will a procedural approach only approximate photographic maps, but building parametric texture layers takes a significant amount of time for large terrains.

I'm sure that many of you may have good suggestions after building your own large terrains. Any thoughts are welcome!

To ground this discussion in some specifics, the full height map is roughly 12K (square) and the photo texture map around 120K square.

Even with Unity tiling tools like WorldStreamer, this would require seamless caching of ~100 2K maps.

Is there a consensus on the upper bound for textures to be viable in Unity running on mid-range GPUs and CPUs?