While I've never w/d from methadone, I have seen others do it, and I from sub. Theyre kinda comparable (at least in timing/length) so I will tell you what I know about m-done withdrawals:
-the first day is not so bad. Its pretty deceptive because with most agonists you feel like HELL 24 hours after your last dose, and w/d usually peak around then, maybe 1.5 days. not with m-done. Which brings us to next point
-the worst day is usually day 3 or later. Depending on how much m-done is in your system, it could even be day 4, day 5, heck maybe even day 6. This is why it is a bitch, because it gets MUCH MUCH worse before it gets any better. Normally by day 3-4 youre thinking "oh shit i'm almost out of this hell!" Not with m-done...
-the withdrawals last quite a long time. its different for everyone, but dont expect to be golden on day 5. Expect to have to walk quite a bit further before you're out of hell
-expect to feel off for awhile. From what I"ve seen on BL, and at NA, people who get straight off of m-done do not feel normal by any stretch for quite some time.
I am sure there is much I have forgotten, but having listed all of this, and I would say methadone might be one opiate where it is actually a BETTER IDEA to taper off with another one first. Thats up to you, and I dont recommend tapering off with a full agonist, as that will just trigger the beast inside of you again. Perhaps switch to suboxone?
A fast taper would probably be a lot less painful than a methadone taper. Both last as long but sub w/d are not that bad. Then again I've been on since jan at 3mg a day so I guess we'll see how bad they are this time, but I'd STILL rather go through that than methadone.