Don't you hate it when someone beats you to post while you are typing... I'm just too slow
Anyway, I was going to say more, but now I will just say that Elite Fexes are Fexes in the elite slot because they have been minimally upgraded and are cheaper, so that a nid player can get 8 MC's.
Also, check Benandorf's Carnifex Tactica, currently shown on the 40kO homepage, because he covered everything