This question is about the performance of using a large texture on an object that is only UVed to use a small portion of the actual texture. I am basically asking, if I have an object which UVs only use 10% of a 4096 texture, is the performance the same as using the full texture? Or does unity only use what is actually rendered? I have an object (FPS hands) that are using two different texture maps, unfortunately the textures are too large, 4096, and the texture is already painted for that objects UV layout. I would really not want to cut out the painted areas of the two texture maps and try and line them up on the new UV layout. I have normal maps as well 
So I would be using two 4096 textures for this one object, but only about 10% of the image is actually used. How does Unity handle this?
Unity will need to use the whole texture, we don’t cut up textures. A simple solution is to open the model in a modelling program, auto unwrap it and bake the diffuse texture to the new uvs.
I am using Maya LT, and unfortunately Transfer Maps has been removed from the baking solution