BMW never claims 0-60mph time. Their numbers always represent 0-100kph, which is 0-62.5mph. So a 0-100kph of 5.1 translates into a 4.9 0-60mph, which is why the BMW times always seem to be overly conservative.
So the difference between the results obtained by the reviewers and the numbers given by BMW are not so far away in reality.
I would guess that for a new model like the 135i BMW would be overly conservative so that they would create a more favorable impression when the reviewers get their own numbers.
