You are correct, the CPU load is at 100%.
Thank you for the tip. I tried it without compression, pretty much the same. Maybe a 15 % increase. I also tried single, big files, but they are not faster. (Trying to compress jpegs, mp3 or Videofiles doesnt make much sense to me, but i can imagine that the compression is useful when it comes to other files)
I even opend an issue once: (https://github.com/syncthing/syncthing/issues/676 ) but I wanted to know experience of other users, maybe with 2 or more powerful PCs in one cluster.
IMHO sending files from a low power CPU should work quite fast, once all the hashing is done. (And i read about Why does syncthing consume so much CPU? )