Turbo Compressor maps people.... would have eased this argument straight away, cause they are real world results made by the manufacturers for their products.
Laz put a top mount in your fozz then put dry ice on top, run 25 psi no sweat at least till the dry ice evaporates
http://www.njsr.org/pics/albums/userpics/10619/BRL3911%20-%20compressor%20map.jpg
yea not for the turbo in question cause i cant be arsed trawling the net for it but this will help you to define when a turbo runs out of puff and just starts becoming a hairdryer, compressor surge etc etc