Looks pretty good.
a) I don't generally advise gemming for Defense if you're already uncrittable.
b) Your Hit and Crit are both on the low end. If you want to up your TPS, I would focus on these stats. Maybe get an alternative helm and use the Glyph of Ferocity and 10% SBV gem and use that as your threat helmet.
c) As much as it hurts, you need to upgrade to Girdle of the Fearless.