Is GUITexture slow on iOS, and would it be faster to use a plane and a separate camera?

I wanted to try to roll my own inventory system, and I want to focus on iOS devices first hand so performance is key.

The way I wanted to lay this out was having an inventory bar permanently fixed to the bottom of the screen. To draw the inventory bar, I'm using multiple GUITextures. I wrote a script to handle drag and drop from the inventory bar onto the screen and that works fine using GUITexture (thought I haven't checked performance for this yet).

However, I've read many a post suggesting not to use the GUI system because the amount of draw calls. Does this apply to using GUITextures or is this only for using OnGUI in your script (is GUITextures using OnGUI in them selves perhaps?)

Or should I stay clear of GUITexture completely and us an alternative?

I want to stay clear of 3rd party GUI libraries for this exercise (I did look at NGUI and it looks really nice, but I want to go this route so I understand it better).

I am guessing the other option is to setup another camera, and draw the inventory background as a tiled texture on a plane.

If GUITexture is a big no-no, and I should go the route of a second camera, should I make each inventory item a plane as well, and would that work without making every item rectangular?