Stock MAF is limited, above some point (frequency of more then say 2400 Hz), in providing ECU with an accurate information about the "Mass Air Flow" coming into the engine. Well, it has been discussed before… but as a general rule of thumb don’t go over 0,9 bar if you don’t have other mods. You will either get fuel cut, lean out or get “diminishing returns” in terms of additional power…
PS: Anyway our turbos are working out of their efficiency range, if pushed above 0,9 bar at higher RPMs. They can provide more air, but at cost of heating it... but thats another story.