I have pretty much no opioid tolerance, but extensive experience with pharm opioids. I have Crohn's and had a major flareup where I got my docs to, over the course of a year, bring me up to 100 mg of hydromorphone / day. A surgery later, I was tired of the rollercoaster ride, so I switched to methadone, which I still abused to hell. After four years of that, I got my dose down from 65 mg to 20 mg / day, and cold turkeyed that with almost no withdrawal. (I suspect the moderate amounts of DXM I was doing near daily, i.e. 500-600 mg, prevented the withdrawal.)
A year after no opioids, I felt that I still needed something for occasional pain, so I got my doctor to give me Tramadol. I find it is complete garbage and has virtually no recreational potential, at least for me. I've tried taking up to 600 mg at a time, and I'm lucky if I get anywhere near what 60 mg of codeine would probably give me.
On the other hand (O/T), I picked up some U-47700 three weeks ago (ROI oral, up to 45 mg / dose, 2-6 doses per day), and that was AWESOME. Probably the best opioid I've done. I was intent on self-control, but that didn't pan out quite so well, and I binged through the entire gram in about a week, with one day off. Great week: motivated and happy. Exercised a ton and barely felt compelled to eat, and dropped 2 kg.
Have 1g MT-45 here as well, which I haven't taken, as the stories on these boards about long term effects seem terrifying and I just can't put something that toxic into my body.