Question:

Running a week-long program, it processes 40,000 records an hour running alone
on the weekend.  It process 60,000 an hour when busy during weekdays.  What are
the most likely database settings that could cause this symptom.

Answer:

Seems strange.

The only explination i can give is that on the weekend, a
dataload may have been going on and an index or two disabled to
allow the dataload to go faster.  The index which was disabled
is used in your code hence runs slower on the weekend.
The disabled index is then re-enabled later on in the weekend.