No need to mention "7" in the PC world, since we know a SCSI peripheral isn't normally setup for using "7" (older SGI boxes reserve "4" for its SCSI controller).
Once SCSI-2 was introduced, highest to lowest in SCSI priority became:
7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8.