I've used the 4 inch, excellent quality, allows full lock to lock turns, strong as hell, I'd buy another.
I also have a 4 inch haven't gotten far enough in my build to test it out yet but they seem to be a good quality axel. I'd buy another when the time comes...
Not to answer your Question, but we have two Socal 4" axles and the beauty of these is you can run stock stubs and steering arms, Though you do need to get their own spring also as the perch eyes are a little closer together. So they get you there. More drop is not always better.
I know that it gave your customer's car a great stance! Sent from my iPhone using The H.A.M.B. mobile app