Oxymorphone is pretty damn potent on its own (depending on ROA's it can make the BA vary though). No need to throw the hydrocodone in with it (again just my opinion).
What's your tolerance like?
If you're only used to hydrocodone than oxymorphone is a giant leap from medium strength to one of the strongest they give (besides fent and a couple others.. here ill give you a link for some insight on what im talking about) https://en.wikipedia.org/wiki/Equianalgesic
According to that chart, 10mg hydrocodone is equal to 3.33mg oxymorphone and that's with oral dosing and the BA of the opana being only 10%. Other ROA will have higher BA's. = more potent per mg.
Careful on dosing.