I must say that using right btrfs format command is really important, recently i format my disk with
this command and mkfs.btrfs -n 65536 /dev/sdX (X is a partition number) and i see really increase in performance now it take 2 to 3 hours in comparison 5 or 6 hours in the past!
Thanks!
What exactly did you measure, full image backup time?
What about file backup with lots of files of all sizes?
It can be faster, with the drawback of consuming more memory.