If you don't need 180 Watts of power for your sidings from the PH180, then limiting the max current to 5A would offer more protection for the trains on those tracks, combined with TVS. From another recent post, I saw that you already have TVS diodes connected to your ZWC outputs.
To my knowledge there have no been posts indicating which breaker is faster, but they are probably very close. The trip time for the Airpax "Instant" is 0.1 second in a overload condition.
Also of note: with one Z1000 you'd only need one breaker. The only reason I mentioned 2 was the pricing per unit for more than 2 is slightly less than buying 1 or 2.
