Your father built up a fantastic collection. My condolences on his passing.
Personally I like to avoid going into the secondary market. As Sham mentioned, a 5950R or one of the minute repeaters would be something rather special. Alternatively you can look at the romantic and charming 6102 and 5131 references, or 5740R would be the obvious choice to continue the luxury sports timepiece theme.
Once again, a beautiful collection of incredible Pateks!
Rahul