Nonsense. The only "measurements" that we have so far for the speed of Gravity are the orbits of planets around moving Suns, which indicate speeds orders of magnitude faster than Light for Gravity waves.
"It's worth listening for, but my guess is that advanced civilizations will be using Gravity waves rather than EM waves."
Why? Gravitons are billions of times weaker than photons and travel no faster than light.
Nonsense. The only "measurements" that we have so far for the speed of Gravity are the orbits of planets around moving Suns, which indicate speeds orders of magnitude faster than Light for Gravity waves.