lurker's comment: Btw, I think we might be getting a bit carried away talking about taking the city. If we think we can pull off the city without retaliation that's great. But usually, the way you do these things is to declare war the second you get a horse, and whittle your enemy down to 0 reinforcements. Then he's got nothing in the way of you and his cities. Also keep in mind, you may want him to declare on you, so you don't get labeled a warmonger. Easiest way of doing this is settling near him, then give him the bird when he asks you to stop settling near him. Settling near him also gives you the advantage of easy healing.
Of course, maybe he'll be a pushover on king, never know :/
Of course, maybe he'll be a pushover on king, never know :/