RTFM!
Its 120nm. And you shouldn't 'guess' it as overtightening can be just as bad as not tightening them enough - metal fatigue (in the bolt), damage to the wheel by creating high stress points and stripping the thread in the hub...
And as for impact wrenches - if you see a tyre fitter heading towards your locking nut with one of them punch him immediately. Very hard.
One Spanner Monkey destroyed my locking nut (albeit a different design) on my MGF years ago and didn't bother telling me. I found out when I was descending Hardknott Pass in the Lake District and clipped a rock puncturing the sidewall of the tyre. Words could not describe my thoughts of what I would do to said Spanner Monkey when I discovered what he had done... Rest assured it did involve his impact wrench...