Well done on opening that tin of worms!
The drive shafts always want to run in a perfect straight line to the diff, the faster the car the more that effect will occur.
So, running unhappy driveshafts / \ will mean the car will squat more due the the drive shafts pulling the wishbones up and in effect, softening the rear suspension. This is why raising the gearbox on an X-6 gives more drive.
Running happy drive shafts \ / will do the opposite.
With CVD's this effect is less, so when driving through a corner and the driveshafts are like this \ \ the wheels can still spinup without the straightening force as much as Losi dogbones will.... this is how the two driveshafts are used as a setup option. (and to be honest, I can't feel the difference).
There are so many variables, and if your bones and outdrives are worn - there'll be no benefit of using this as a tuning option as the driveshafts will always want to run in the peak of the worn section and lock the suspension solid (almost) when lots of torque/revs are going through the wheels. Therefore its also important to not have any tight spots on anything that is meant to move, and I mean ANYTHING.
Chris