http://en.wikipedia.org/wiki/LIGO
Check up, they are already testing it. So far the results are showing that gravity waves travel at c.
I am here at Hanford but with no special access to LIGO. Where are you getting the above information? LIGO has not yet detected a gravity wave much less measured its speed.
If c is the maximum detectable speed given our tech, then could it be going c+, but we just cannot measure it?