So just to clarify that:
You'll use feedback from players, completion speeds, successful completion rate, monster stats and your own gut feelings to say that, say, the present live server version Epic Bargain of Blood (arguably the easiest epic) is CR 21 and present live Epic Servants of the Overlord (arguably the hardest 6-player epic) is CR 25.
Then you'll adjust mob stats so that 'new epic hard' BoB has similar but slightly lower mob/trap stats and call it a CR 20 or 21 dungeon, and do the same for 'new epic hard' SOTO and call it a CR 24 dungeon. CR 37 Drow Warriors might fall to CR 35, losing ~10% HP, 2 SR, 1-2 to each save, 4-5 points of To-Hit, and have damage dice dropped from (guessing here) 4d12 to 4d10. A trap that is DC 49 for ~320 damage (Lords of Dust epic blade traps) might become DC 46 for ~270 damage. And a boss with ~90000hp (Crateos in Snitch) might have a haircut to 70000.
And for 'new epic elite' you'll be across-the-board upping mob stats in a similar fashion rather than adding new 'surprises' like the Dread Hex Wraiths in Wiz-King?
(AFK, plotting XP farming strategies for Epic Claw of Vulkoor...)