There shouldn't have been any need to double transplant. Your plants from the 6 packs should have gone directly into your hanging baskets. If you remove a good portion of the root ball, it will result in a pretty unhappy plant! Water and nutrients are taken up by the roots, and they support the plant. Remove a good portion, and the plant suffers (equate it to removing one of your lungs). You should easily be able to fit 3 4" pots into a standard 10" hanging basket without removing root mass.