Here's a render in Maya with the reference images visible in the background.
For the next step, I created a Normal Map using Z Brush to help capture some of the details, like the folds and wrinkles of the eyes, ears, lips and shirt. Here's another render in Maya with the Normal Map applied. The mesh is the same 1,430 poly bust with which I started, only with a Normal Map added.
For the final touch, I created a Texture Map using the high resolution source images of the subject seen in the background. Unfortunately, due to my poor UV unwrapping skills, there are several areas in which the textures are distorted. However, I definitely learned from my mistakes on this one, and I know that my next attempt at UV unwrapping will be infinitely better.
Here's another Maya render from a different angle. Note how the normal map around the ear reacts to the back light as if the intricate ear geometry actually exists. The actual geometry of the ear is nothing more that a shallow, concave "dish."
Although a normal map can definitely spruce up a model, the 1,430 poly mesh in Maya can't really compare to the 1,464,320 poly bust in Z Brush. For a better look at the glorious detail I sculpted in Z Brush, I've attached a few more screenshots. First, here's the head with a basic material applied.