In a thread on BG, testing on "+ interruption % rate" gear lead to the discovery that at 102% you will not be interrupted by a melee hit. Knock-back, stun, terror, or movement can still interrupt, but standard hits will be ignored.
Saw this on another board and got me to wondering if this would be worth maxing out Iron Will. Iron Will when maxed out gives 95% -spell interrupt to not only yourself, but the whole party.
This effectively means just macro in a pair of Valor Breeches whenever Rampart is up and you can get any spell up you desire i.e. Stoneskin, Utsu, etc.
Now I'm aware Shield Mastery makes this a bit less useful, but I still see it being more handy in those oh-sh*t situations than say Guardian.