I assume that you did your shoot already, but I figured I'd answer for the sake of posterity -- I personally would shoot 720PN in AVCi for downconvert. There won't be an appreciable quality difference between 1080 and 720, but the files in 720 will be half the size, which means the cards last twice as long.
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc. blog.abelcine.com