I've personally done a bunch of testing on this issue....and found that the individual piece of lumber makes more difference than what the grain orientation is.
Here's another perspective, and relates to the strength/stability issue.
Aerobatic aircraft use spruce for the main wing structures...and the main spar is quartersawn...since the spar is usually 6 to 8 inches tall by an inch wide, the grain lines are PARALLEL to the forces exerted on the wing under stress. Or in otherwords, at a right angle to the forces exerted on a quartersawn guitar neck.
It would seem to me, that when true strength is needed, the stress needs to be parallel to the grain line, rather than at a right angle. However, the reason quarter sawn is used is that the tendency to split is GREATLY reduced, rather than the slight advantage of the "strength" issue. This also applies to acoustic instrument tops, where the wood is so thin that stability and resistance to checking is of great greater concern than absolute strength.
Further, while I've worked on only 3 Lakland basses with the bolt on quartersawn necks, ALL 3 were highly unstable; not due to the quartercut, but rather to a lack of baseline stability in the neck lumber itself.
I will have to admit that part of my skepticism is due to my lumber inspection process while I was the process engineer at Peavey's guitar factory...I literally looked at thousands of necks over my 3 1/2 years there...and believe me, a good piece of wood makes a good neck, regardless of grain orientation.