Probably somewhere between those two extremes.  I don't know that there is one real number because of differences in timing and human error.  I would take those two numbers and average them for a probably 5.0-5.2 second 0-60 time under normal conditions.

In the User's manual of any 3-Series BMW there should be the 0-60mp/h (or 0-100 km/h) values, for all models (X or not, Automatic/manual gearbox). That was the case for my E46 and it was the only way for me to know, as no magazine or website reviewed this particular model (330XI Touring automatic gearbox). So if you don't own a 3-Series, stop any driver on the road and ask to see his manual ;)