Backspace for Caprice Wagon?

Im getting ready to order some 20s and 22s for my wagon and need to know what backspace to get.  Anyone have any idea what i should get?  Below is my choices. 20x8.5 with a 4.75 or 5.25 backspace22x9 with a  5 or 5.5 inch backspace

I'm kind of wondering the same thing?  I'm just going to run 20's but i need to what width and backspace I can have with a bagged and bodied caprice wagon.

impalassforum.com has the answers.