Well, as it turned out the motor and ESC came wired the wrong way (not like I asked to have it wired ...), i.e. it's spinning in the wrong direction.
Googled a bit, because I already had the feeling that just swapping two phase wires wouldn't be okay because of the sensors.
Looks like I have to try six combinations for the phase wires and six for the sensor wires. So in worst case, I have to try 6x6=36 combinations :(
Here is some info on sensor and phase wiring:
http://www.endless-sphere.com/w/inde...rushless_Motor