"If the speed of gravity were infinite, Kopeikin predicted that the quasar should have traced a perfect circle in the sky as Jupiter passed. If gravity had some finite speed, this circle would distort into an ellipse."

And, one assumes, the deviation of the shape of the ellipse from a perfect circle would reveal something about the amount by which the speed of gravitational propagation falls short of instantaneousosity?

If one imagines the momentum of Jupiter distorting its gravitational field--its "spacetime dimple"--in a manner consistent with retarded-field theory, then one can get a feel for how the perfectly symmetrical circular figure produced by deflection of the quasar's light under a non-retarded-field regime would be transformed into an ellipse. Or so my mind's eye insists.