first, if you want the best server to client and vice-versa interaction, then none contends better than Spoutcraft(client) and Spout(server-side Bukkit Plugin), the only draw back is that they will always be a little behind Vanilla client(one version of difference), right now they are at 1.2.5 but they should update soon enough, it's just a matter of patience.
There is already a plugin that allows you to add Items and Block to the server. plus there is no need to work with archaic pseudo client mods in order to use better optimization, Spoutcraft already comes with that and more.
Also, whitelist me and send me IP.