5DMKII or 1DMKIII for weddings???

I'm new to this forum but need help making a decision on my next camera.

My apologies if this question has been asked before but I couldn't find my answer in the search of prior threads.

I currently have a 40D and would like to upgrade for weddings. I have the following lens:
16-35 2.8
24-70 2.8
70-200 2.8 IS

I know there are pros and cons with both cameras but for those who currently own one or both I wanted to ask your advice.

What I like about both is:
MKIII - dual card slots for back up mem.
High IQ and all the rest that comes with the "pro body" but cost much more.

5DMKIII- Full frame, high res. LCD and all the new bells and whistles but no "dual card slots”. Plenty of MP but a need for more memory cards although still less than the MKIII...

I have not used either camera before but would again ask for advice from those who have for weddings/portraits.

Thank you,
Julie J.