He said, 'The theory of relativity is often criticized for giving, without justification, a central theoretical role to the propagation of light, in that it founds the concept of time upon the law of propagation of light. The situation, however, is somewhat as follows. In order to give physical significance to the concept of time, processes of some kind are required which enable relations to be established between different places. It is immaterial what kind of processes one chooses for such a definition of time. It is advantageous, however, for the theory, to choose only those processes concerning which we know something certain. This holds for the propagation of light in vacuo in a higher degree than for any process which could be considered, thanks to the investigations of Maxwell and H A Lorentz.'
Is appears that many have taken the speed of light in vacuo to be the limiting speed of material objects, and that this may be an error of great significance for the progress of physics in the past century. SR describes how motion of material objects may appear.
According to observational evidence, the speed of propagation of gravitational force may well exceed that of light by ten to the tenth power — see http://www.metaresearch.org/cosmology/gravity/possiblenewpropertiesofgravity.asp for more.