I want to add something- just HAVE to although the post is old, only catching up on old ones lately

ZANZ Richard, ALL of us know how you feel, but there is a big difference between the people thinking about immigrating and those that actually do it. You and your wife both need to be 100% committed to immigration. If one of you are not 100% committed that person could be very very unhappy on this side. You should think about the ages of you children in 4 years time, the older they are the more difficult it could be for them. My daughter was 15 when we arrived and compared to my son, she struggled a bit. It took her a year to get into the kiwi way of doing things.
As others indicated, you have a gift with your PR, some people will kill to have that but it is still your decision. We tend to get into a comfort zone in SA regarding our lives there, we don't want to make more sacrifices that we are already making on a daily basis just to survive there and I believe it is not normal for a person to choose inconvenience, we all want to be comfortable and immigration is not a comfortable situation to be in, to feel comfortable again in NZ takes a while and the sacrifices are immense.
In SA we don't have as many choices as people from other countries moving to NZ, we can't go back because our decision to make the move is different from theirs. Immigration for me is/was an abnormal decision process since no person has to decide between their own children and their family and friends.
Goodluck with your decision!