1, 2, 4 & 8mg Dilaudid pills are Instant Release type pills, while the 20, 30 & 40mg Opana pills are Extended Release. As far as the 10mg Opana pills go, they are availible in IR & ER form, there are 5mg Opana IR's as well.
When taken orally, Oxymorphone has a Bioavailibility of approximately 10%, while Hydromorphone has a BA of approximately 30%.
Oxymorphone is 1.5X stronger then Hydromorphone mg for mg when IV injected, but when you factor in the Oral BA of each drug, Hydromorphone is 2X stronger mg for mg when taken orally.