A question about draw call performance when it comes to unique texture use.

I was wondering what sort of hit on performance one would experience when using an atlas texture for many batched meshes, and then use the same texture for dynamic meshes.

For example, say I have a 4096x4096 atlas texture that I have made for many static structures. I have some left-over texture space in this atlas to use for a dynamic door model that will be used many times but obviously can't be statically batched. To simplify my example, the dynamic meshes can't benefit from dynamic batching.

Now my question is:

Would it be beneficial for performance, to make a separate smaller texture for my door models, or include the texture in my big atlas texture.

Should i make a new texture for unbatched meshes, or can I use the "free" "real estate" on an atlas texture?

To clarify. Say all the static meshes are combined into 4 draw calls and all the doors are sent out as separate 30 draw calls. will the huge 4096x4096 atlas texture be sent 30 times between the CPU and GPU, which will be bad for performance? Or will the texture only impact performance once, and I essentially get to use free real estate on my large atlas texture and won't have to bog down my computer with an extra door texture even though I don't get the benefit of batching on my dynamic meshes?

I would really love to get some more technical information about the issue since Unity's own documentation is a little bit vague on this subject.