As I understand there are two issues in the question:
- the category as defined by certification (max wt, config) - the speeds flown as recommended by the manufacturer.
- the category to be considered in operation with respect to safety margins required by PANSOPS or TERPS (n.b. not always the same); e.g. where config / speed is changed for operational reasons, then use the category according to the revised values.
The first aspect is generally considered as an economic issue.
The second, much more important - safety margins in operation.