My personal concern is that the improvement in physical damage reduction is so low in relation to the amount of damage that we take that it won't significantly alter our survivability, particularly in 25s where overheals are the standard, anyways. The Mastery increase, assuming the 1 Mastery = 2% Armor, means we need approximately 20400 Mastery (or ~68%) at a base armor of 82529 (which is what I currently have in Bear form with iLvl 521 average, ignoring Mastery). However, half of that Mastery still gives us almost 72% armor, and can be obtained pretty easily through gear and buffs. Even now, with my (relatively low 18%) Mastery and raid buffs, I still sit at roughly 70-71% armor. Best case scenario, we could shave off another 4% physical, which on a 400k swing is what, 16k?