Keep in mind that what you want as a paladin tank is more mastery. Because of the changes to block in Cataclysm, the more mastery we have as tanks the better.
For example, back in wotlk you could basically block every attack with over 60% block chance in Wotlk. In Cataclysm, they changed it so that you have 30% chance to block at all times. Mastery only increases that 30% chance of block to work. Meaning that the more mastery you have, the more blocks you'll have.
For a clear idea on your defensive stats, you need around 112% ( 112% = dodge+parry+block) at level 85. Out of all the tanks, we're the ones that dodge the least. First being feral druids. Our specialty is blocking.
(I was the guild tank, so I know my stuff!)