Hi there!
Newcomer on my first post, just hijacking the thread to quickly post my impressions.
Today I spent around two hours A-B testing the PM-3 against the DT770 PRO (80Ω, so expect differences, especially in how small portable devices can handle these compared to the 32Ω), the A900X and my old M50. Thanks to Jaben, in Melbourne to let me play with that stuff for such a long time.
Short version: they sits in a totally different leagues. I drove these from my mobile phone unamped (a Nexus 5) and, while I do agree that it was an unfavorable source for the highest ohmed contender (the Beyers) it was enough to provide a somewhat comparable volume from all the candidates.
HOWEVER, the DT 770 weren't able to keep up the pace. I am nowhere near an audiophile, but I can guarantee you that the difference between the DT 770 and the PM-3 (or the A900X) was perceivable.
I hand picked a few tracks I know pretty well, a mix of Classical (Prokofiev's Dance of Knights, Tartini's Devil's Trill and Chopin's Raindrop), a Skrillex track (Make it Bum Dem) and an Italian one (De Andrè, Un Blasfemo). Especially, and surprisingly, on the last one, the DT 770 showed some limitations, the same suffered by the M50. All of these tracks are in high quality, lossless format (apart from Skrillex track).
In "Un Blasfemo" there are some sections in which the deep voice of the singer mixes with the medium-high trebles and THERE you can see the limitations, simply put in layman's terms, the driver is unable to clearly provide the whole picture and the result is distorted output, very noticeable on the voice.
If you are up for just fun listening from unamped mobile (or low powered) sources, then the DT 770 Pro 32Ω may be a better choice for you (the pleather pads on these will also probably provide you a free bass boost compared to the velour pads on the 80Ω I've tried today).
If you are up to an higher level of details and quality from good sources, then maybe you would be better trying other alternatives (PM-3 included). Keep in mind though that, despite the low reported impedance level and power needed for the PM-3, my Nexus 5 was barely able to push these at medium-high volumes.
I cannot provide direct comparison with the volume output of the DT 770 80Ω, but it was equal or better; I can certainly guarantee you that my old M50 almost shoot my brain out when I kept the same volume I was using to test the PM-3
I am 100% sure that a portable AMP/DAC (like an E17 or similar maybe, to stay in the "affordable" realm) would have improved considerably the experience I had both with the DT770 and the PM-3 today.
If more impressions are needed, just let me know. I am currently losing hours of sleep to digest the differences (and similarities) between A900X and PM-3...so I may have more inputs for you should you have specific questions.
To eventual more experienced readers, forgive my lack of terminology and probably a few grammar errors here and there...I'm here to learn!