i say standard 16g but get an ecu first then can have it mapped or do what 20 said an get a z4 you will not need to upgrade engine parts or gearbox an clutch an you can prob push the boost up a little an get around the 300bhp mark your only problem if you want to go a little further will be injectors as they will be on there limit if there standard
an it does seem like fuel cut as 20 said i have a spare boost gauge if you want to plump it in an see what you are hitting mate