Interestingly, a higher number of gears is best suited with motors that have very narrow power bands. Mostly small bore engines used for racing. This way, at any upshift you stay in the meat of your powerband. I used to have a Euro 635 CSi with a souped up 4.0 litre motor from Metric Mechanic. That engine would put out 300HP and 300ft.lbs of torque, and all that at a very low RPM. The 5 speed close ratio was a PITA as te motor had too much power and torque to use the close gears. I was shifting all the time for nothing... The M5 V10 is hardly a small bore motor with a narrow powerband.. I guess that deciding to include 7 gears may have to do with marketing and wanting to impress at show'n'shines... That makes for one more "upgrade".