Any individual bit could be noise, so it might take 2-3 bits to transmit something unambiguous (via an error-correcting code or similar).
If so, I think the speed advantage disappears.
If so, I think the speed advantage disappears.
If you wanted to transmit a lot of information with one pulse, you'd use time domain slicing and synchronized atomic clocks.
Regardless, you don't need particularly high signal fidelity in order to arbitrage the market, just better than 50/50. The ~25ms they can cut off of the transmission latency is an eternity in market time.