I honestly have no idea what you guys are talking about... the numbers you state look almost random.
F3x:
BMW claims 4.9 sec 0-100 for xDrive and automatic gearbox. I for one have not seen people do appreciably faster with a
stock car and measured with Dragy! If there is a record of this anywhere in the forum - please advise.
G20:
BMW claim 4.4 sec 0-100 for xDrive, automatic gearbox, limousine
The difference in power delivery is 48 PS and 50Nm in favour of the G20.
0,5 sec reduction in 0-100 sounds about right to me
Maybe some minor difference in the gearbox shifting contributed to 0,1 sec out of that, but generally it sounds about right.