For that you will have to go North to the Loire valley.
When you come to South Africa the Sauvignon blanc you must try are
Steenberg
Jason's hill
Thelema
Klein Constantia
Neil Ellis "Groenkloof"
Buitenverwachting
These are very good but different in style to each others.
Steenberg reserve is my fav but pricey at around 12 US$
Jason Hills best value at around 4.5 US $
Cathedral cellars is made by KWV which is a huge co-op and although the std is good they are not the best.
Cheers
Serge