I've got both the SE 535 and the Bowers P7, unfortunately my SE535s are no longer in original shape. I upgraded the sonic filters on them and the cable. The Bowers p7 are original unchanged. Since you only provided 3 points of comparison between them i'll try and answer as best as i can for you.
- Both headphones are extremely clear. Instrument separation and vocals are unbelievably clear and will detour you from 99% of the headphones out there once you've lived with either for a while since nothing in the non-audiophile world will be able to satisfy you. The Se535 with a set of acoustic dampeners can change its clarity. They have the ability of going from harsh, excessively clear headphones (gray filters) to being very close to the signature of the P7 with a mild warm sound yet still maintain clarity in treble and a tight bass (brown filters). If i was to choose only a single headphone based on clarity it would the SE353.
I know you didn't ask, but dynamic range is also something interesting. The p7 outperform the SE535 here. This is also to do with the fact that the p7 is somewhat colourful whereas the SE535's are a little more flat in response up until the highs. The P7 does have a phenomenal way of creating shift in sound while not going overboard.
This one is easy. IEM<Closed Back<Open Back
There is no way around it. No IEM will ever come close to an Open pair of headphones, my Grado's have a sound stage that make either look like a dorm-room. That said for IEMs the SE535s have a very good soundstage and for closed backs that P7 have a very very good sound stage. So the P7 sound stage will win over the SE535 here.
Another for the p7 i'm afraid but i say that only cause you'll be in Iran. The SE535 cable IS replaceable but the connectors on the ends are not generic. You can't find the ear plug cables everywhere especially where you may not have access to the online market. The p7 cable, though oddly shaped is still a simple 2.5mm to 3.5mm cable that is more likely to be available locally and cheaper. For basic SE535 cable your looking at $30-40min, upgrades around $100-150 and overprices at around $500. The P7 Cable can be replaced directly from Bowers for $20, upgraded for around $100 and overpriced to only god know how high.
If i had to pick between the two as my only pair it would be the SE535, but not because of your criteria. The SE535 isolate better so better for both louder environments, leak less sound so better for quite areas, more portable so easier to carry when travelling, moving around etc, gym use, and less cumbersome to easier to have in your ears when just going about doing things than the Bowers P7. I've lived with the SE535 only for 4yrs and have no complaints, well sorta, had my grado's :-) but only got the closed hp's a few months back.
hope that helps...