I missed your post above. I have two FF6s, one is set up for 3s and one for 6s. I can confirm that your power draw around 700w is correct. I suspect that your Multistar packs are probably bad. Many of the Multistar packs have been found to be over-rated on their 10C discharge capability. That being said, I use the same packs but mostly for the more efficient 6s setup.
This winter, I will also be interested in converting my 3s setup to APM. I may even convert it to 6s since my SunnySky motors have dropped in price. Here is a video of the 3s maiden flight from February. I could pull the logs from it if you like.