So I made earpad swap. Admittedly not until after I validated from Oppo that I could still get replacement earpads if I needed them.
(For those interested, $39 for the earpads, $49 if you send the PM-3s to them and have them install them.)
The first thing I noticed was the pads no longer touched my ears. I didn't think that was an issue, but I guess it was. Definitely more comfortable.
I also found that I turned the volume up a bit more. I expect this may have something to do with the additional roominess but that's just speculation on my part. I've only been listening for a few minutes but my initial thoughts are very positive. I don't feel like there's any loss of clarity, but there's definitely more space. I'm going through my usual test tracks and the difference is noticeable. It's possible some of the edge may have been taken off the guitars on Megadeth's Countdown to Extinction, but it's subtle, if at all. Dave Matthews Band's So Much to Say and Dire Straits' Sultans of Swing both seem to have more breathing room. I've got a lot more listening to do, but I'm glad I made the change. I can definitely recommend it.
Thanks much to
@big_scot_nanny,
@FastAndClean and
@SteveOliver (and others I may have missed) for the helpful posts.