[zipdog]

As I understand it, Einstein's work rests on there being a fundamental maximum 'speed' and it seemed to him as though the speed of photons was that limit, so 'speed of light' became synonymous with this maximum. But it doesn't necessarily have to be so.

So if there's something faster, it changes our understanding of photons but not the existence of this fundamental maximum speed.

As you note, our efforts to measure c may have been off due to measuring the wrong thing, but I don't know the ramifications of a small % change in c.

(I'm not a physicist)

[kaybe]

Yes, it is -the- basic assumptions for special relativity. And no, it doesn't just change our understanding of photons, it changes everything, since it's all connected. All theories I've looked at so far have (at least in higher versions) incorporate relativitity.

(Another basic assumption, this time for general relativity, is the equality of inertial and gravitational mass, which is not a self-evident thing. However, so far no difference has been found. (see http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment)