Thought I’d check on the Linux source tree tar. zstd -19 vs lzma -9:

❯ ls -lh
total 1,6G
-rw-r--r-- 1 pmo pmo 1,4G Sep 13 22:16 linux-6.6-rc1.tar
-rw-r--r-- 1 pmo pmo 128M Sep 13 22:16 linux-6.6-rc1.tar.lzma
-rw-r--r-- 1 pmo pmo 138M Sep 13 22:16 linux-6.6-rc1.tar.zst

About +8% compared to lzma. Decompression time though:

zstd -d -k -T0 *.zst  0,68s user 0,46s system 162% cpu 0,700 total
lzma -d -k -T0 *.lzma  4,75s user 0,51s system 99% cpu 5,274 total

Yeah, I’m going with zstd all the way.