As I tried to explain before, experiments have confirmed that gravity propagates at the speed of light. This is why relativity is a superior theory to Newton's theory of universal gravitation - by accounting for the finite propagation time of gravity, it perfectly models the motion of the planets, whereas the Newtonian formulation has some small errors.
Would you care to provide a link? Last time I talked to a physics prof, there had yet to be an experiment to prove this. One problem with looking at Newtonian physics is that we're using light to measure things by, and light is deceptive.
I thought for a long time about what Einstein said concerning the issue, and after close to 20 years of considering it, I have come to the conclusion that it is false. Gravitons, I believe, travel at an instantaneous speed. There are no benchmarks to measure the graviton. As far as science is concerned, it's never been tested. At least, I haven't found one.
This is how I imagined Einstein's talk about going at the speed of light. First, I created 3 reference points along a line labeled A, B, C, and gave to each a clock that kept perfect time. The distance between A and B is 100 light years, and B and C 100 light years. Then I had fun with point B. Point B travels towards point A at the speed of light. Two perspectives will be created. Point A will see point B for 100 years, ticking away 100 years behind, when suddenly, after 100 years of traveling at the speed of light, the clock jumps to a synchronous time. Perspective C, after 100 years, the clock on Perspective B (as it travels towards perspective A) moving at 1/2 the normal speed. This is, of course, after 100 years of watching it, and this would continue for 100 years. Time doesn't bend, it's just our perception of it as is delayed by light.
The problem, I figure, with modern physics, is that it demands too much from light. It is used to formulate the rules of the universe when it is deeply flawed. As Plato put it, "Don't believe everything you see." (paraphrased, obviously)
Light is no different from sound. If you were on a ship traveling at the speed of light and you shone a light ahead of you, no one would see it until you'd gone clean past them. Then, at best, there'd be this infinitesimal brief burst of light followed by darkness. If the light was omni directional, the person watching the light would see not just light in front of him/her, but also light behind him her. Let me put it this way, if you did this for 1 light year, you'd see the light after it passed you for 1 year, and you'd see the light as the light emitter continued past you. Of course, this is forgetting the idea that the red shift would likely render any light invisible.
I liken the whole misunderstanding to that of a world of blind scientists trying to say that nothing could move faster than the speed of sound (something that was said even when we could see) simply because the sound of a jet never changes speed, regardless of how fast it travels. If two people with synchronized clocks were to measure speeds of the sound at different locations, they might talk about how strange it was that there was a sound heard before there should have been. That is to say, if there's a jet going at mach 2, and the sound reaches someone in half the speed expected, then they'd have to make up some kind of confusing science, inventing such things as worm holes and other bizarre tales created to try to explain the inconsistency.
Gravity travels at an instantaneous speed. This much has become clear to me since about 2 years ago. I began pondering how strange it would be that the earth in its orbital pattern would be following not where the sun is, but where the sun was 8 minutes ago. I then further speculated that this 8 minutes would see a variable depending on where it was in orbit. As you know, the sun itself is in orbit and is moving at a tremendous speed. If it was, for the sake of argument, traveling at 1/2 the speed of light, then in those 8 minutes the difference of where the sun would attract the earth would in fact be 4 light minutes when at the furthest point in the sun's path, but would in fact be physically closer to the actual sun when ahead of the sun in its path around the galaxy, causing in fact a fluctuation, or harmonic, which, coincidentally, would be physically impossible if the sun was in fact moving at 1/2 the speed of light. Now, you might suggest, and correctly so, that the sun is at best estimated to be traveling through the universe, with everything tallied to the highest estimate I've found, at only 1/300 the speed of light. Certainly, this is true. However, if you consider that some particles have orbits as well, and they also are attracted to a center, and if they themselves *do* travel at 1/2 the speed of light, then the orbiter and the orbited could not help but collide.
My conclusion is that light is simply the fastest measurement we have in looking at the universe. Since we use it to determine physical truths from the universe, and we know that it is flawed (after all, we see the sun as it was 8 minutes ago, not as it is), it seems silly to create absolute truth, such as that as the speed of light being the maximum, based on it. There is no reason to believe it if simple common sense is applied to it. Logic dictates the universe, not our flawed reasoning.
Check this out:
It points to experiments that prove that the minimal speed of gravity must be 2x that of light. Of course, I believe it to be instantaneous, and therefore fallacious. Nonetheless it shows that there is far more doubt over this issue than what you purport it to be. Furthermore, it goes a long way towards supporting what op said.