They are saying their dyno is an extremely accurate dyno. A $250,000 dyno that is of the same type BMW itself uses. That the car on 91 would be around 525 HP ( 550 HP on 93 as BMW rated), and with mods my mods on 91, I'm at 556. Hence an approximate 30HP improvement. Thus the results are just as expected.
They've mentioned other subaru's make 420 elsewhere and put 360 down here.
Anyway, that's the story. Obviously with no stock runs, there is no exact measurement of mod increases.