Option to select the preferred graphics processor is greyed out for IE but available for Chrome and Firefox.
This is expected behavior with all drivers after 337.19.
The Optimus profiles for Chrome and Firefox use the iGPU by default to provide maximum power savings. However, you can force it to run on the NVIDIA GPU by using the program settings in the NVIDIA Control Panel.
The Optimus profile for IE still requires it to run only on the iGPU. A profile settings update will be available in the future that enables this same functionality in IE.