So #4's for each hot, a #4 for the neutral and a #4 for the ECG. Correct. Cb on separate phases. I'm not sure but I think both gate openers will operate together. I sized the #4 for starting amps for each motor. Now that I digest this I should size the conductors for running amps at 8.5 each reducing my wire size to #6's.
If it's two gate openers for opposing gates, most likely will operate at same time.
You are correct, size for running amps typically, you have to make sure the motors will not stall upon start (most likely will not).
Another option...
2P
15A circuit breaker
(2) 10AWG, (1) 10AWG GRD
8.5A load at 240V
2.8% Vd
3kVA XFMR 240PRI/120SEC at load end
25A rated secondary current
10AWG secondary conductors to loads, considered protected by primary OCPD.
Ohhh... you'll also have to drive two ground rods at least 6' apart and run # 6 to one leg of the transformer secondary.
Price it and make cost comparison including labor.
Breaker size corrected above.