It's about a 5-6% loss, so yeah, it's about even with BM.
But then again, compare BM to your Dps Shaman, BM has free mobility and an immunity on top of Bloodlust.
Yeah my bad, at least one Mage needs to unequip the ring.
True, haven't checked MM (much) on Beta.
But stilll, it just proves the point: There is nothing special about Bloodlust when 3 classes can cast it.