Quite often Maya will slow down when working with image planes in your modelPanel. Here is a script that will generate a separate image plane camera and assign it to a referenced layer while you work out of another camera to speed up viewport performance. You can run the script multiple times to generate more than one image plane for each camera, too.

Update 0.1: Fixed an incorrect camera setting.

This is an automated script based on a tutorial I've written on my website: http://www.dezfx.com/HTML_Pages/TutorialPages/imagePlaneCamera.html