It was rumored a while ago on SSC that they were thinking of adding some floors to the South Tower. (Again, rumored, don't quote me on that.)
The 525' figure obviously wasn't final for this tower so maybe the 950' isn't final for the South Tower, or they'll combine the two other towers to make one 500+ meter tower (in my dreams).
It would be nice to see 1200+ feet though, it's the perfect location for it.