Hi,
I also tried creating the table as "UNLOGGED" which led to walwriter I/O to drop drastically and I now get no wall-clock time increase with two import processes but it gets slower with four.
Switching off fsync leads to a drastic time improvement but still higher wall-clock time for four threads.
Thanks for the pointer to the other mailing list. I'll try my luck there.
Cheers,
Manuel