Yeah, his early rush is tremendous. Another bonus that he has is that his super early culture boost (both from unit production and mines) allow him to reach Agoge (+50% faster unit production speed) and Political Philosophy (+4 combat strength from Oligarchy) very early, and that further boosts both his ability to produce a large blob of archers, as well as further boosting the strength of any melee unit blocking ahead of them. Stack all those factors together and you have one hell of a strong rush potential. Rushed down Cyrus in my last Deity game with that opener, and I'd say that is pretty impressive since Cyrus is among one of the worst opponents to face when you want to rush someone (due to Immortals having a ranged attack and still decent melee strength). Gaul is no joke in the early war department.