besides bodyweight, the difference in the transmission and engine affect too..
you could debate about N54 vs N55 .. N55 is newer design with single turbo, one guesses BMW was thinking fuel efficiency and lowering cost..
you would have to try both back to back keeping everything else constant, but no bmw is configured like that i think
some say N54 is more performance oriented, N55 better efficiency (newer) with 'similar' performance .. we can only guess
i liked the 135i when it came out.. so small with all that power
