2c/3 is a respectable speed in the Life universe; by comparison, a glider travels at only one-fourth of the speed of light, and it was proven many years ago that this is the fastest that any finite diagonal spaceship can travel through empty space. There is a similar limit of half of the speed of light for orthogonal spaceships.
However, disturbances in pre-existing structures can travel much faster than these limits -- there is no theoretical limit lower than lightspeed, either diagonally or orthogonally. See Gabriel Nivasch's lightspeed article for details and examples.
A signal in a 2c/3 track will quickly overtake a glider travelling in the same direction. If a sufficiently long track can be made to turn a corner, a 2c/3 signal in it will even overtake an orthogonal c/2 spaceship.