Sorting out Sort key strategy

I (we) am loading a lot of data into a detail data set in IMAGE with a sort key.  Do I presort the data by the sort key only? Or do I presort by the Automatic key then the sort key?

As in:

Entry                    Offset

BP-EXPLODE#        X10     1  (!BP-EXPLODE-A(PRIORITY))
BP-BENEFIT           X10    11  (BP-BENEFIT-A)
COMPONENT          X4     21
RIDER-TITLE           X8     25
YMDEFF                  X8     33
YMDEND                 X8     41
PRIORITY               X2     49

I know this really improves performance.

Ray Shahan replies:

Since your sort key is at the end of the data set, then you need only sort by the sort key value.

Denys Beauchemin adds:

Sort by BP-EXPLODE# as the first key and PRIORITY as the second key within BP-EXPLODE#.