Any reason against the shures other than design?

IE800s have better bass (and sub-bass), other than that it comes down to preferences. I prefer Sennheiser sound signature.

I see, and how long will the sennheisers last? I'm interested in the 800 or the 846, durability is what concerns me about them most due to the cable being detachable only halfway

IE800s bass is emphasized, so "reference class without any coloration" is not an accurate description. Also, you didn't include any comparisons (besides the SE846), so I can't tell where the reference claim comes from.