Will try out Macro weapon swapping but I remember it being a pain in the past.
From what you're saying- would I be right in paraphrasing that: after a certain stack point I should swap to max stam? or Mystic/Dawnblade combo is more effective pre stacks regardless?
Glad to have some math based theorycrafting, thanks for stopping by.
A lot of it, as Hashbrowns says, comes down to personal preference. Numerically, you're always going to be better off getting as much mitigation as possible (For example, say you have 30% physical damage reduction. Well, you may not take 100% physical damage, but if you take 37% physical damage and 63% magical damage, then you still have (.30 x .37) 11% flat damage reduction across the board).
That being said, you get 25% reduction from magic damage just from being Guardian Spec. You get 12.5% physical reduction, and a 200% increase to Bear Form armor. Logically, the reduced physical reduction is supposed to be made up for by the Armor Increase.
Therefore, armor is important to Guardian because it makes up a sizable portion of what Protection Warriors get as a flat 25% reduction. (Sidenote: This is what people talk about when they say Protection has more base mitigation. Protection has high armor and a 25% physical reduction, making it slightly superior against Physical Damage than Guardian's 12.5% physical reduction with high armor. The numbers do not innately balance out).
That being said, Bear Form also supplies a flat 40% increase to Stamina (Translation: each point of Stamina gives 14 health instead of 10), which makes Health also scale superbly for Guardian.
Brutality Stacks - There isn't really a mathematically sound way to calculate which set should be used or at which point. Think of it like this: If you have 1000 health and 50% mitigations, are you better off than having 2000 health and 25% mitigations?
Say that you're taking 500 DPS, and your healer is able to put out 350 HPS. The 1000 health 50% mitigation is going to numerically be superior to the 2000 health 25% mitigation ( every second the healer has a surplus of 100 HPS versus every second the healer has a deficit of 25 HPS ).
However, this is numerical superiority and doesn't quite translate to a real situation. Having 2000 base health makes you far less likely to get "1 shotted", something that healers have no chance to help you defend against. When Healing is extremely powerful (which it still is from the perspective that the HPS of a Hpally or a Rdruid is something like 800 while spamming heals), it is better for you to have a higher health pool than it is to have higher damage reductions.
tl;dr:
Stay in Bear Form.
Giant Health pools are probably going to be your best option.
Keep both sets, just in case of future changes.
Brutality Stacks ADD a damage increaser that is not affected by your mitigations (75% damage versus physical, with brutality becomes 175% damage versus physical).
Oldspike and myself have found that Stamina seems to be the best route to go. For Prot Warriors, using the BoAs gives so much armor that it is hard to argue against it being BiS over Mystic's Robes. However, for Guardian I'm not so sure.