Low, low low low, low, low, low low low low low, low, low.
You will also need to consider induced noise on a long wire. Noise could, and will, cause false level detection at the other end. Shielding the wire will surely be necessary if you run the wires through your house wiring.
High speed cabled communications is a rather involved subject...At higher frequencies you have lots of things to consider:1. The resistance of the cable2. The capacitance of the cable3. The inductance of the cableAll these add up to basically form a low-pass filter, which limits the maximum frequency that can be transmitted down the line with minimum attenuation.