I've taken 1000mg of 100mg IR Tapentadol in a day, but I wouldn't recommend that unless you could take 200+mg of Oxy and still be ok. I've never injected or done heroin, but I do have a high tolerance. Usually when I look at these forums this is the kind of answer I would want. If you had never taken opioids before, even 50mg would give you a buzz, if you do it frequently but not everyday 300-400 would be a decent dose. The difference in instant release and modified release makes a massive difference, if you are experimenting with instants, try 100, wait an hour see how you feel. I also like both and legally prescribed oxy and tapentadol together, 40mg oxy, 200mg tapentadol and my country is really strict on controlled medications, so I assume that dose might be considered "safe" according to the doctor.
If you hit the ceiling and take more you will only feel nauseous and will ruin it. Please be extremely careful, this is my experience not advice.
"Most clinical studies have suggested that tapentadol 50 mg has a similar efficacy to oxycodone 10 mg. However, for drugs such as tramadol and tapentadol that have other mechanisms that contribute to their analgesic effect, it is essential to consider analgesic equivalence rather than opioid equivalence"