Beyer pads do not fit on the R70X. Beyer pads have a very thin outer lip which does not go on them.
I have multiple Brainwavz pads. The custom hybrid velour, the HM5 (oval) velour, and the XL micro suede. All of them are larger than the stock suede pads. The custom hybrid and Hm5 velour alter the sound a lot. I like both of those more on the DT770s, especially the custom hybrid. I thought those sounded awful on the R70X. The hybrid has an inner perforated leather liner, and velour on the outside that touches your head. They make the R70X sound hollow, which is quite an achievement.
The XL suede does fit though it is a bit large, but I have not had any issues with them coming off. It is very, very similar to the stock pads in sound to my ears while adding some much needed breathing room. I have the normal one, not the memory cooling gel. So it likely compresses about the same as the stock pad. Judging from how much better the micro suede sounds than the hybrid or velours, I'd guess the material has a lot to do with the sound signature with these, since the inner diameter of the stock pads is more similar to the smaller custom hybrid and HM5 pads.