I often do large par repairs for two reasons:
1) I often grab very old posts -- up to 5 years old -- even using 3 NSPs (2 as fill servers), there are often broken files.
2) I get large posts every day (40GB+) -- these can be slightly broken on all
NSPs -- maybe two files have 1 block missing, for example.
If I see that par2lib is taking too long to repair, I will cancel the repair and repair using par2cmdline (multicore).
I use the following command:
That lets it use 2GB of RAM (I have 8GB on my NAS) and speeds things up a bit. It would be nice to have multicore repair within nzbget, but it's not the end of the world.