Since you have lots of data you can use parallel loading.
Split your data in several files and then do :
CREATE TEMPORARY TABLE loader1 ( ... )
COPY loader1 FROM ...
Use a TEMPORARY TABLE for this : you don't need crash-recovery since if
something blows up, you can COPY it again... and it will be much faster
because no WAL will be written.
If your disk is fast, COPY is cpu-bound, so if you can do 1 COPY process
per core, and avoid writing WAL, it will scale.
This doesn't solve the other half of your problem (removing the
duplicates) which isn't easy to parallelize, but it will make the COPY
part a lot faster.
Note that you can have 1 core process the INSERT / removing duplicates
while the others are handling COPY and filling temp tables, so if you
pipeline it, you could save some time.
Does your data contain a lot of duplicates, or are they rare ? What
percentage ?