Okay, so I don't think this is a repost, i searched it. I have not tested this due to the fact I don't own a private server, just had the idea. So step by step ill show you how to easily make new stats for tiers on your private servers.
Step 1: you must have a program that can recognize and follow patterns, I'm using Microsoft Excel. I will be making the Warrior helmet for tiers 7-9.
Step 2: Take the stats you would like to have included in you new armor, and put them into a spreadsheet like this.
Step 3: Select one collum, in this case it "Armor":
Step 4: Pull the sqare in the corner down 3 spaces. This will follow Blizzards pattern in the stats for the tiers:
Step 5: Do this will all the other collums:
And it should look like this.
Step 6: Round off the stats:
Now I would suggest that you would follow Blizzards pattern of 3 tiers per 10 levels.
Hope this helped!
-Banmaster