I think a lot of guys go off of pressure for rating blown motors when volume should be the major concern, a standard 6.71 blower may make 12 Lbs. of boost at 600 HP at 6000 engine RPM and by changing the blower and slowing it down with 8.71 or 10.71 will make 200 HP more at the same or less pressure and RPMs
Same thing on turbo sizes