To answer the couple of questions/posts I see since last I've checked see the following.
I always used either suboxone or methadone to taper then switched to something short acting like oxy or morphine.
As long acting opiates like sub or methadone have longer w/d times. So I taper using them & then use oxy or morph.
Just for a few days to a week till mdone or sub out of system then I jump.
When I jumped off 120-150mg Oxymorphone nasally I felt better after a week, relatively normal after 2.
Though that was a completely different jump. I cold turkey'd it & also gave up other drugs / cigs at same time.
Paws / no proper sleep / pain (I have pain issues to begin with) came back & I relapsed after 2 months.
Ended up doing all the same things again though had I realized how bad my habit would get I would not have restarted.
I was trying to control pain issues but I now realize the pain is better than the constant battle of dependency.
I'm currently tapering again off a much larger habit. 100mcg/hr Fent Patches + other opiates on top via IV.
But I digress, that's my issues not yours.

Just wanted to answer your question regarding time-frames.
Now as for the Suboxone questions. I'm not as familiar as I've not had as good luck with suboxone as I do methadone.
Though everyone differs & lots of people feel the opposite. I found Suboxone more useful when I had a lower tolerance.
The literature would concur as Suboxone has a ceiling dose/effect. However with your tolerance this shouldn't be an issue.
I've used Suboxone maybe a few months total over the course of a few years spread out between various occasions.
Though most of my usage was when my tolerance level was closer to yours & as such should be more applicable.
Less is more with Suboxone & one can get by on surprisingly low doses. Regardless switching off Oxymorphone
chances are you will have some w/d's for a few days before you adjust. As Oxymorphone seems to be worst for w/d's IMHO.
I would use the Suboxone for a quick taper & then either do something short acting for a few days or just jump.
Depends how low you taper the Suboxone & your person physiology.
You may be able to jump straight off with relatively little in the way of issues it varies person to person.
I see you said
That will get me through 4 days without withdrawl symptoms and hopefully everything will be out of my system by then.
I may be misunderstanding you or perhaps you are misinformed. Having everything out of your system doesn't mean w/d's are over.
When everything is out of your system is when the real withdrawals start.
As withdrawals are a result of your body lacking what it's used to. Not from removing a "toxin".
Suboxone (Buprenorphine) is a partial agonist. As such it is still an opiate.
So when taking Suboxone you still have opiates in your system.
As a partial agonist it should be milder to w/d from. Compared to Oxymorphone I'd say it's definitively milder.
When your done tapering the Suboxone then you will experience w/d's as you won't have opiates
(Suboxone in this case) in your system anymore.
Due to the long half life of Suboxone w/d's may take a day or 2 to really kick in.
However they will be milder than Oxymorphone w/d's are / would be.
The Suboxone (Opiates) won't actually be out of your system for likely a week or more due to the half life.
This actually should help your w/d's to be milder as the opiate leaves your body more slowly.
Allowing you to come off more gradually & hopefully have an easier time of it.
Hopefully that information helps you & if I had more time I'd elaborate more. I'll try to keep on eye on this thread regardless.
Also since you seem to be going with the Suboxone route I would highly recommend giving the following a read.
Suboxone & Buprenorphine Mega Thread & FAQ-v13.0
The above thread is full of great information regarding Suboxone, tapering, maintenance & good discussions regarding them.
If you have questions regarding Suboxone & tapering & what not; that thread is a great place to start or post.
Hopefully I've helped answer your questions a bit & I wish you the best of luck with your goals.