as far as i've seen, I believe drops to be the same at 55 as to 70 and onwards. Mirror Mazes would be prime suspects for "big" drops if better drops at 80+ were the case and i've not had anything interesting drop in them, however i've not completed that many.
I would argue your best methods are either welling with high magic luck, or group explore climbs starting at 55 and finishing at 65-70, depending on how good the gear of your group is.
(whistle 1-55, at 55 start explore at 70 stop explore and go back to whistling) we do this semi regularly on softcore when we have enough warlocks/alchemists in the group. Sometimes start at 45 or use a high EP map.
The group explore climbs can generally slaughter large groups of EP's quickly with extremely small amounts of downtime. doing it solo usually means you spend some time regenning/shrining.