with a vacuum leak its going to run horrible more than likely. what kind of manifold and turbo are you running? also what about exhaust. obviously and i may be stating the obvious your exhaust is what powers the turbo if your engine isnt exhaling properly your not going to spin that turbo adequatly. my expertise is mainly from nissans primarly the rb25 but a turbo setup is a turbo setup. if the turbo is too big or the exhaust is impedded its going to slow the spool. also is the turbo a journal or ball bearing? journals will also spool slower. but tend to be cheaper. your graph looks to be pretty linear though. at least to me.