I've gotten it above 50 so far and the challenges are starting to dip below 90%, even for my extremely endgame stats. Rewards are still in the 1.5 Echo ballpark, so it's looking like slowly grinding Secret Miracles up into the thousands for ridiculous EPA after several years of sacrificing your favor cards for terrible EPA .....isn't going to be a thing.

UPDATE: The highest reward I've gotten so far is 390 Jade, at 69 Secret Miracles. That's not *terrible*, but it's only a lucky roll at the high end of the possible range; the average will be much lower. Especially considering that the Dangerous check has now dipped below 70%.