Dreamer,
You can run 70 with a MM. Here is a video of a I-GT running on 4S I had built and sold a few months ago.
http://www.youtube.com/watch?v=YRkRL97is2E
This was done with a MM, Feigao 7L on FP 4S packs. I would suggest you not run anything smaller than an XL can to help keep the heat down!