I am not sure what a Light version of Aero is. Are you running some type of minimal version due to graphics limitations?
What does the Experience score show now for the graphics. The overall score doesn't mean much since it goes by only the lowest one.
If you let Windows adjust the settings, it will pick the one it thinks is best... Depending on your setup, it might reduce performance.
There are trouble shooters you can use to check your systems performance, beside the Experience Index. Maybe it would give you some information you don't currently have.