I use the .9 AI's, and I like them with four shelves in each one. Granted, there is a pretty big temp change from top to bottom, but I use that to my advantage since I change temps by small amounts throughout my purge process regardless..
Also, I went down to lowes and had them cut me custom 11"x11" squares out of some marble and some granite tiles. About 3/4" thick. Cost about ten bucks for four 'shelves'
and the thick marble or granite will hold temp much better than the standard racks, or even the solid ones for that matter.