IOS GUI optimization

When using unity for IOS they suggest that OnGui is not used as it will greatly decrease the performance of a game. Basically they state to avoid this if you can. However, the details were a bit vague.

I have a simple 2D puzzle style game that requires only 1 GUI to pop up sometimes during gameplay, however the speed of this GUI is imperative.

What I'm wondering is whether I should create this GUI as a game object instead of a GUI (in my case this won't be hard + with orthographic camera you can't tell the difference) and control it with a ray from the mouse.

Looking for the fastest results if anyone is knowledgeable in this domain.

Thanks.

Do not confuse OnGUI() with the rendering components like GUITexture and GUIText. They can exist as standalone GameObjects that do not use the OnGUI() method, and perform well on mobile devices as far as I know.