Then again, perhaps all that they really measured was the speed of the radio waves bending around Jupiter... No, they took that into account (of course).
But the point is that the incoming radio waves would bend around Jupiter in slightly different ways if Jupiter's gravitational field "instantly" followed Jupiter around as Jupiter moved in its orbit, versus whether Jupiter's gravitational field lagged a bit behind it.
If instantaneous, Jupiter's "gravitational lens" (which was bending the incoming waves from the distant star) would be spherical, whereas if gravitation travelled at the speed of light, it would be subtly "conical", like the sonic boom coming off of a supersonic jet. The two different "lens" shapes would result in different kinds of "warping" of the incoming waves from the distant star, thus allowing the experimenters to answer the "is it or isn't it" question they were posing.
Pretty clever.
"But the point is that the incoming radio waves would bend around Jupiter in slightly different ways if Jupiter's gravitational field "instantly" followed Jupiter around as Jupiter moved in its orbit, versus whether Jupiter's gravitational field lagged a bit behind it."
Their admitted margin for error in the experiment was .25 times the speed of light, a figure far too large to measure speeds drasticly greater than C.
My money is on Isaac Newton. The Speed of Gravity is far more likely to be substantially faster than the Speed of Light because gravity easily bends Light while Light does not appreciably bend Gravity.
If E=MC^2, and if Gravity (G) is equal to the Energy of a Mass (i.e. G=E/M), then G=C^2. Thus, I'll go with Newton and speculate on a much faster speed of Gravity, along the lines of the Speed of Light squared.
All that this experiment measured was the speed of radio waves as they bent around Jupiter. Gee (pun intended), that's the speed of light!