Saw on Edmunds -
http://www.edmunds.com/bmw/4-series/...oad-test1.html - an instrumented test of the 428 / 8-speed auto where they were getting 0-60 times of 5.4 seconds. Car & Driver's current issue has similar results.
Wondering why the X1 sDrive 2.8 doesn't match this performance as from what I can tell they have the same engine and the transmissions (identical ratios per the BMW website). The difference in weight is negligible (3470 lbs. for the 428 and 3527 for the X1 - again, per the BMW website).