Several times during raids in ValorA t6, ValorB t7, and ToT Lobby t8, I've held aggro and tanked for over 5%, usually with one beefy cleric (thanks Arieanna) keeping me up while we sort out whatever issue put me as the temp tank. And I'm at 20.4 stones.
Something to consider, though, is that I've put a heavy emphasis on AC. There are many t7 and t8 monks who have 100 or 200 less AC than me, so it's all about how you gear your toon. And keep in mind that I've had a powerful guild backing me up since day one.
An underweight monk on tier with a a bard will win every. Single. Time.
In my opinion, if you don't have a good guild, you're going to struggle finding gear for your monk. It seems a lot easier to bring a bard to a given tier than it would be to bring a monk.