I Don't know the answers to your Question, other than that Morphine is strong and hard to come off of...
I Wanted to say that Ms contin is working REALLY well for me. Once I got used to it. It took about a week or more but now that my dose has been tweaked 3 times I am finally at a level that my pain is at a 4. Which is great.
It's working better than the Oxy at this time.
I take the MS Contin ER ( morphine sulphate) 3 times a day and I take morphine sulphate IR 2 times a day as needed. so far I haven't needed the B/T meds but 3 times in the past 7 days, so its really a GREAT pain reliever.
I would want to try Morphine before the bigee methadone. But that is just my personal opinion.
I am sorry to hear the oxycontin isn't keeping up with your pain. I haven't seen a post from you since you heard your GP had asked you to see a PM Dr. So I didn't know it wasn't working well..I always had a feeling your GP would do this since he was so far away and didn't have many PM patients.
I do think this is a good thing in a way because it was always an issue, and the drive was just to brutal and he was just to far away and not a specialist in the field of pain and that is what I think you really need. With winter upon us imagine that drive of 6 hours in the snow or a blizzard. Yikes.
All the best in your search for a Dr and getting the right pain relief.

Slippery Slope.