We will see if the 4 cylinder is really a 1/2 second slower than the 35i after someone does a true road test with the car and publishes it, such as Road & Track or Motor Trend.
BMW has already overestimated the 0-60 time for the 35i. The 35i does 0-60 in 4.7 based on tests. It is faster than the 5.0 BMW claims. Meaning the 4 cylinder will have to do a 5.2 to truly be a 1/2 second behind the 35i.
A 1/2 second is still signifigant in the 4-5 second range. The faster car would be noticeably faster if watching such a race.