Originally Posted by KoenG
Just did a "moron" calculation: When the RWD would have perfect 50/50 weight distribution with about 758kgs per axle, and the extra 75kgs of the Xdrive are 2/3rd (808kgs) on front and 1/3rd (782kgs) in the back, the distri changes to 51/49%.
So actually, we're really nitpicking here I gues, well beyond the sensible difference in dynamical behaviour to my opinion, or your name should be Vettel or something.
Back in the E30 days, it was quite easy to feel the difference between the short four cylinder engine (318iS) and the long six cylinder engine (320i) from the driver seat. The difference in overall weight and how it was distributed was quite small, but the cars felt very different. The inertia from the added mass plays a part as well.
I would guess that the difference from the AWD would be similar in the F20/F21, but you would have to test it to see.