Were you told about the run in? On the F30 they told me that's not needed.
But yeah I took the G20 on the motorway and tried xtraboost on and off and for sure there is a torque difference between the two, and the BMW genius beside me didn't seem to mind me pushing 190
G20 is 6.5s to 100 according to BMW UK site, where did you find 5.9s since on paper is technically slower. I've asked BMW this several times and no one knows why