This is the reason BMW uses the "Guibo" for the center joint. Its lighter than a U joint and helps dampen the drive line harmonics. Center bearings don't really impact the amount of torque to turn the driveline, at least the ones I've worked on spin like nothing. The weight is a good point...
I agree a seven piece drive line would be total overkill, but your not necessarily saving energy with a one piece drive line. It goes in and out of harmonics at varying speeds, its pure luck and your driving style that determines the effect
Now using Guibo's instead of U-joints might work on some cars,, Just a thought there...
Oh well it was a thought, if it makes 50MPH at the end of the salt flats there should be a gain somewhere... its also the reason so many cars used to crash, drive-line would whip and tear the car up... Of course that was at silly speeds, not what were are talking about.
Dave