You get three tiers propagating at very different speeds: The machine intelligence - spread solely over the airwaves to receptive civilizations, which then get

You get three tiers propagating at very different speeds: The machine intelligence - spread solely over the airwaves to receptive civilizations, which then get taken over to promulgate further spread. Laser launch telescopes have great bandwidth and transmit at approximately the speed of light, but require some selectivity. The intelligent machine - Robotic Von Neumann probes, probably of the star-wisp design. Can colonize barren rocks, and be sent out in large batches at low speed. The intelligent race - The fleshy bits. Not even very interested in barren rocks compared to planets. So logistically difficult that the supporting infrastructure limits them to tiny fractions of the speed of light at the cost of large fractions of civilizational output.