I think you're the FIRST person I've come across to talk about that treble spike in the SE535. For the longest time I'd talk about the SE535 being harsh, borderline unlistenable for me, and most people would just say "huh..." In the end, I started thinking it was just fit, and maybe I'd never get them to sound right. But it looks like you're hearing it too. I heard the same thing with the older E500.
I've kinda come to like the Pro 50. It's still too bassy by half and the mids could be a bit more upfront, but its nice tone, good detail without fatigue, and just pleasant overall presentation have won me over. It's a very good "plug in and forget" type headphone, made even better by stellar comfort and good overall build quality. It's a bit more sensitive to eartip type than I'd like, or was used to in the UM3x, but there's a good selection of usable tips that sound good enough and that's all I need.
Very descriptive, I know, but not wanting more out of your portables is generally very high praise, considering that the only full-size headphone that made me not want more is the SR-007. The Pro 50 is far from perfect, but its faults are easy to live with, especially on the go. Now they just need to drop the price to something more sensible ($450 or so would be just right).