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 effort an extraordinary gyroscope is needed. Launching a spacecraft from Earth demands a huge expenditure of energy. Yet, compared to electricity, gravity is unbelievably weak.