Given how itchy it is, I didn't try to blow through it or anything. It's pretty lightweight, though, so I suspect it breathes quite a bit.
Whether it's the additional material or the pressure against the driver, this is the best treble I've had with these mods by a long shot. Once that material on the back of the driver is removed, it's really hard to get a good level of treble that extends all the way up. This version is great, though, nice and sharp but not harsh at all. It's hard to quantify the difference here, but it's definitely the best. They are a bit more forward, and it emphasizes the speed that orthos are capable of delivering. The soundstage seems a bit more coherent as well, probably because I've finally gotten rid of that midbass hump It's pretty big, too, which I think might be a perceived larger cup volume with the rock wool.
Some people might find this setup a bit too bass-heavy, but it doesn't impact the rest of the sound range, similar to what I've experienced with the Thunderpants so far. This is some of the best headphone bass I've heard, though. The bass has speed and impact, and you can hear where it is coming from in the sound mix.
Too bad it's hard to get the Roxul in small quantities... I had some around from my renovations this summer.