Consider the whole package
I like the N55, as I did the N54. I am still not sold on the 4 cyl. THe numbers are impressive and on a test drive it was fine but noisy (X1) I did not test it in the 5 series.
THe one that really surprised me was number 4 on the list. The Pentastar. I drive it in a test of a Jeep and found it to be very badly programmed. THe power was there only the engine management system made you wait while it seemed to ask "Do you really want to leave economy mode, your fuel economy will suffer, well don't say that I did not warn you"
As consumers, it is a whole package, the engine management system, the transmission and the engine. That is how it should be. That is why BMW is so great, they look at the whole. I would not get on a plane if the pilot said "Today I am going to concentrate on airspeed." I want the pilot to balance airspeed, altitude and navigation. Well is it similar with a car. Nice to have a good engine, but have it drive the rear wheels etc.