I was wrong, it's 57-60% home field.
Coin toss came from here:
https://www.reddit.com/r/nfl/comments/2h30h8/statistical_look_at_the_new_ot_rules/
So essentially winning the coin toss is the same as getting home field advantage for the OT.
Edited by Zeaux at 13:29:31 on 02/06/17