Short answer, this:
Quote Originally Posted by Yotsu View Post
http://i.imgur.com/fUhcIpt.png
Long answer:
Full i90 with enough accuracy for your target content vs BiS parry based difference is pretty minimal. If you're currently gearing up then it's pretty simple, if you get a higher item level tank piece than the one your wearing and not drop below your accuracy target, it's an upgrade. If you get an equal level tanking piece that has more parry than the one your wearing and not drop below your accuracy target, it's an upgrade.

Proper answer:
Farm to Philo and Myth cap, then ask again next Thursday.