rear bumpstops height

I am looking into getting the Durobumps, but trying to figure out which height bumps I need and want to see if someone can help me make sure I am doing this right. According to my measurements, I have 9.25" between the top of the leafs to the bump stop strike pad. The total axle up travel is about 4" until the shock bottoms out. I read in another forum where the vendor who makes the Durobumps said that "during crawling and while articulated with the weight of the truck on the bump stop, they compress approximately .75". It varies by situation and truck weight of course, but thats a fair number for us to work with". I am guessing the compression could be more than .75". So, to me that would mean I would need at least a 6" Durobump. Is this correct?

 

Anybody?

 

whats the update?