I am pretty sure gravitational waves are propagating with light speed as the maximum limit to the spread of information as well.

Hence two objects beyond each other's oberservational horizon would not affect each other in terms of gravity and current assumptions about our universe is that it is alot larger than the observable part we can see.

This fact is also critical in the early creation of the universe where the pattern within the background radiation was analyzed based on the fact the "clumping" of hot and cold areas would be limited by the propagation of gravitational waves and hence allow interpretation from it to the geometry of the universe.