I know this is an old thread and I dont even own a 370z but this info may be relevant:
Stock 2009 Infiniti FX50 S AWD Dyno Sheet Details - DragTimes.com
I believe your 7at is the same as in the fx 50 which appears to dyno at 329hp and 299lb-ft on a dynojet according to the above dyno chart. Torque tends to be more important then HP in transmission longevity so it stands to reason that if it can handle a stock 5.0l fx50 with 299lb-ft it probably has some engineered in cushion for more torque. Granted that was a dyno jet and not a mustang dyno..... hope this helps
EDIT: off to my regularly scheduled lurking... see you all in 6 months.