I'm currently slogging through "Faster than the Speed of Light" by Joao Magieijo that goes to the implications of the possibility that the Universal Constant may be wrong. Lots of evidence in the Event Horizon that that could be. Now this. General Relativity? Anyone? Anyone?
Only thing that needs to be clarified is that: c is the fastest possible speed a photon(or any particle without rest mass) can achieve in a vaccuum. You can only decrease the speed by manipulating the geometry of its wave.