How does one align texture maps of Multiple sizes and resolutions on same sphere? I'm creating the classic "Pan away from Earth" animation and would like to arrange it so that detail levels are more or less constant throughout the animation.  

The problem I'm having is figuring out how to map these textures on my sphere in such a way that they line up properly.  

Right now I'm borrowing the full size NASA Earth image textures, which work fine when my shaders are not too complex.  However, when I add several more layers (clouds, bump map, normal map, my own additional textures and so on) at the same resolution, my 4gb GPU can't handle the strain.

To solve this, I'd like to create several different resolutions of each texture, and then stack them on top of one another in a single texture.  I would then crop the higher resolution textures around those points near to where my camera will begin its "journey" to reduce the GPU strain.  I would then map the whole Earth with a relatively low resolution texture for when it is needed. 

Unfortunately, I cannot figure out how to map the "cropped" images.  Right now, I'm cropping them in Photoshop before importing them.  However, when I map them "spherically" they are stretched to the full size of the sphere.  Playing with the texture mapping utility is difficult, and sliding around UVs manually is hopeless.

Is there a simpler way to do this within Blender?
It sounds like your images have some blank space once you've reduced the resolution. If you simply get rid of that space and make the whole image smaller blender should automatically scale the UVs relative to the image size.

What I mean by this is that if your UVs on the full resolution textures go right up to the bounds of the image, if you have a texture at half that resolution and size the UVs should just be scaled down and still go right up to the bounds of the image.

You can see how I mean if you take a lower resolution image that has no empty space and replace a high res image with it.