I've yet to do further testing with said engines and how the number of engines affect speed, although that is on my to-do list.
As for the first row being ever-so-slightly further, that is the result of the soft-body handler glitching a little (normally extended connections like that are not possible, but would you know it, the building method for the engines can result in said glitch occurring) due to the symmetry of the creature (the devs did state that the handler hates symmetry).