Since Unity3.5, the way to boost your fps over 30 fps on IOS has been changed.
The old method is making change on appController.mm
#define kFPS 30.0
#define kFPS 60.0
in XCODE, after you build the project.
The new Method is by using:
Application.targetFrameRate = 60;
If your game is optimized for better performance, this should increase your game’s fps over 30.
There are other elements involved with game performance, please check out Unity Web site at :http://unity3d.com/support/documentation/Manual/iphone-performance