Working with Modular Rocks
It's easy to unwrap and stitch the newly extruded border faces in max.
I simply split them up in top/down, left/right and relax each piece, then I start stitching the edges and making sure the actual rock UV will not move, because if it does all cracks and such will be offset from where the mesh was split up.
After the capping I will still need to try and get rid of as much ugly intersection (blue painted) as possible when repeating the mesh.
You will not get away from having quite some overdraw ingame working with these kind of meshes. It is simply a matter of how usable the set should be vs. having minimal overdraw.
When you have a pretty nice cap of the borders you can offset your units from each other a lot more ingame which will make the set a lot easier to use and it will be easier to break up repetition.
Just to give you an idea of how much you can do if the engine you use supports vertex colors I made a variation of the texture with no real crack defenition.
I then really quickly assign vertex colors to my mesh where the cracks are modeled.
This way you can really create any shapes you want and even use a smaller texture which is tiling more often over your mesh.
In 3DS Max you can either select vertices when in Editable Poly mode and then assign the vertex color of your choise to those vertices selected.
Or you can simply add a Vertex Paint modifier and paint directly on your model.
You can also bake out ambient occlusion and assign the result to the vertices. You may get some weird results if your mesh is not quite well tesselated tho.
It can be a good way of getting a base up to render out the ambient occlusion first and then manually paint some extra where you like.
Some Additional Thoughts
Whenever I have been working with large chunks of more organic sets I think one of the first questions you should ask yourself is HOW your set will be used and seen.
There is a tremendous difference to create a set of rock walls if the player will only see them from a maximum range of 1-5m.
However if you will be able to see the same rock walls from a distance of 100m+ and heavily repeated next to each other you will also have to base your whole set on that requirement.
I have often, especially when working with rocks, made the mistake of making them way too busy in general.
Something I noticed, when working on a game where the focus point would be around 30m from an object, is to work zoomed out in 3DS Max, Photoshop or whichever application you use.
This way you can quickly concentrate on the right amount of details right from the start instead of spending countless hours on details no one will see.
Here I just added this mesh in Unreal.
And this is the version with a flat texture and vertex colors assigned.
These are some more examples where I have used various ideas and techniques brought up in this tutorial.