A little known fact is that parallel XZ do compress worse than XZ !
I measured pixz as being approximately ~2% worse than xz.
That's because input is split into independent chunks.
In comparison, the 0.8% of zstd looks like a bargain.
In comparison, the 0.8% of zstd looks like a bargain.
zstd is used at level 20, but it can compress more. Levels can go up to 22, and (complex) advanced commands are available to compress data even more.