Everything is still the same because you are squeezing power from a higher octane fuel.
over 300/320kw your afms will be maxxed, you need a free flowing exhaust
Dont know at what boost -7's stop being efficient
all you need to do is,
explain how the car is misbehaving
when does it do it (cold, hot)
does it boost fine
can you hear any noises that your not meant to
what mods
I fear you have to many problems and if you want any sort of help you need to give detailed descriptions of the whole mechanical condition of your car.
PS: Beat you Mr Mad