To the best of my knowledge, there is currently no experimental evidence of the velocity at which gravity is propagated. Due to the tiny size of the gravitational constant, direct evidence of the propagation velocity of gravity would be extremely difficult. Direct measurement would have to involve large masses moving at high velocity with respect to one another, using equipment to map the changes of their motion due to their mutual gravitational attraction. By determining the amount and direction of force needed to make the course changes observed, the velocity of gravity could be estimated reasonably well.
However, the installations which have been built to detect the existence of "gravity waves" would give an indication of the velocity, especially if they can detect the origin of such waves. Unfortunately, they have yet to get a positive detection signal.