There are plenty of people running the 2-port variant making the same power levels with an equally smooth curve as your 6-port.
Is it too late to get your money back?
FWIW, I think there is an inherent flaw with a bottom mounted/ stock placement turbo. I just moved to a top mount pushing more boost than ever.. checked the charge pipe and it's bone dry. (Never saw that even on a bone stock setup)
This car's been out long enough, there are plenty of brackets built specifically for this car personally I wouldn't risk it.. Bride, P2uned, Titan come to mind but I'm sure there are others.
You could always ask a place like P2uned if their brackets are universal to other BMW's.
Go back and reread what I wrote.. I never said a piggyback would modify those values.
If you're car makes SOME additional power you do not need to have those values increased since it'll stay within the factory preset.