It was probably already mentioned earlier, but I noticed this only recently => somebody else might have missed it as well.

My syncs are now a lot faster (using new options "--compress-choice=zstd --compress-level=3 --checksum-choice=xxh3"). Output on Gentoo:

  # rsync
  rsync  version 3.2.3  protocol version 31
  Copyright (C) 1996-2020 by Andrew Tridgell, Wayne Davison, and others.
  Web site: https://rsync.samba.org/
  Capabilities:
      64-bit files, 64-bit inums, 64-bit timestamps, 64-bit   long ints,
    socketpairs, hardlinks, hardlink-specials, symlinks, IPv6, atimes,
    batchfiles, inplace, append, ACLs, xattrs, optional protect-args, iconv,
    symtimes, prealloc, stop-at, no crtimes
  Optimizations:
      SIMD, asm, openssl-crypto
  Checksum list:
      xxh128 xxh3 xxh64 (xxhash) md5 md4 none
  Compress list:
      zstd lz4 zlibx zlib none

Synced files up to a size of 400GiB => nothing was hanging (it could happen in the past, for misterious reasons) and CPU consumption was minimal.

Really happy about these improvements.

But still favoring RSH over SSH. That's how dinosaurs must have felt.

Would definitely love to see rsync handle reflinks. I don't think it does this now.