After some fiddling and melding, I got 85% finally with 727 Gathering. 722 was 84%, 701 was 83%. I would hazard a guess that 725 might be the magic number.

My gear at 701 Gathering, which is what I had before I tried to hit this cap, was the i180 MH, HQ i170 OH without melds, full HQ serpentskin set with only 6 total Gathering melded onto it, and the full HQ i170 accessories and belt with 42 Gathering melded across them. I hit 727 by throwing 16 Gathering onto the offhand, and melding +5 onto one of the serpentskin pieces. Had to meld another +5 onto another piece to finally get 727. My melds were sloppy and focused mainly on GP and Perception with the serpentskin stuff, so I am guessing you could probably get the same results without any of the i170 accessories.