Starlight deflection follows from the electromagnetic theory of light plus a special limiting case of Einstein's equations. Third, most important, Gravity Probe B investigates the gravitational action of moving matter. The frame-dragging measurement detects this force and fixes its scale. The frame-dragging effect, small as it is for the Earth, reaches far. Above all, it may throw light on grand unification .
Grand unification is the greatest challenge confronting theoretical physicists today.
The Stanford experiment is especially interesting in that it focuses on the spin. I would not be surprised at all if it gives a result in disagreement with Einstein's theory. But to measure this extraordinary effect an extraordinary gyroscope is needed .