Which parameter settings will execute the most efficiently?

Appending to existing table & delete duplicate records
or
Delete existing tables?

Do I create rows before index?

I've always preferred to delete the existing table where possible.
Create rows before index is faster but carries some risk if the process is halted before completion (see Help file).

if you use the -f option (which is create rows before indexes) then you're temporary tablespace must be big enough to hold the complete index. If not the index will not be created
Bdbpost will not give an error when the table loads correctly and when it fails to create the index.

When using Oracle set the array interface on and increase the buffer to 100: orainit:0101000 and ora_max_array_insert:100

For dumping a table counts the same by settting the buffer for getting the records to 100: ora_max_array_fetch:100 and rds_full:100