Do both signals move at the theoretical speed of light, or are they limited by air/cable friction factors?
Close enough to the speed of light as to make no difference. The chief limiting factor is the number of gateways. Each router on a network acts as a repeater, so it takes a bit of time to process the signal and re-transmit. The more “hops” in a connection, the slower the transmission. You can see the effect by using the tracert command in Windows.
No. Fibre runs around 2/3c. The light doesn’t travel straight along the fibre, it bounces back and forth within the fibre cable.