According to Merck, University of Iowa, Opana ER website, and likely many other sources - 20 mg of IR oxycodone ingested orally is roughly equivalent to 30 mg of morphine ingested orally. From my understanding, Diacetymorphine/diamorphine (pharma grade h) is said to be around 3x strong as morphine - but that's pure pharma grade heroin which is far from what is available on the streets. Potency various like crazy with street dope - you can get some garbage that maybe only contain a single digit percentage of actual heroin, you can get good street heroin that may very well be 30%-50% or even more pure, or you can get something that's cut to shit but has fentanyl and will be stronger than anything else... Also, note that bioavailability of oxycodone is extremely high (many estimates say 80%+) compared to other opiates like morphine which is very low (I believe around 30-40% orally?).
So asking how strong a certain mg of oxycodone (any method of ingestion) is to heroin (street or pharma) is a bit hard to answer. However, based on my experience, I'd say that .1g of high quality IV street heroin would be roughly equal to 60mgs of IV oxycodone.
Also, in my experience, 90 mg of IV oxycodone (3 perc 30's) was about equal to 16 mg of hydromorph (2 dilly 8s) - the rush being a bit more intense with the dilaudid but the high lasting longer with oxy. I primarily did pills while I was living in Florida as H was very scarce at the time and when it was available it was east coast powder that was cut to shit. I had what I'd consider a low tolerance at the time (about 2-3 perc 30's or 2-3 dilly 8's a day). After I moved back to Chicago, which was essentially a 2 day drive, I felt next to no WD symptoms.
I like oxy because it gives me a nice speedy and energetic type of high and it has some legs. However, oxys aren't really popular on the street anymore at least in this area. Many former pill users, including myself, often started out with a legit script and due to the clampdowns on doctors who RX opiates have found themselves using heroin after their scripts ran out, their docs cut them off, due to the large difference in price between painkillers (even if obtained legitimately from the pharmacy) and heroin, or in my case their doc committed suicide after a DEA investigation and other doctors were too scared to write a script for 45 vicodins meant to last 15 days despite proof of being in a serious car accident.
More info on various opiods and their equianalgesic doses -
http://www.merckmanuals.com/professional/neurologic-disorders/pain/treatment-of-pain
Also, sublingual heroin seems like a waste of time... I don't think it would work well and the amount required to produce even a minor effect would have you gagging, spitting, maybe even puking from the ultra strong bitter taste. In my country, some of the old people farmers back in the day would eat little balls of opium or make a to get some pain relief and relaxation from a day of working in the field.