Hi Sounderhd,
For shure 840 it says it is 10ft but it is coiled. I'm not sure whether it means you can stretch it to become 10ft, or when its coiled it is 10ft. However, my friend owns the sony 7506 and when its coiled I think it was fine. Plus the 840's cable is detachable. Shure does a straight wire http://www.shure.co.uk/products/accessories/hpasca1 but it is 2.5m I think compared to the 3m coiled. The HD 25's are a popular choice, however, they are on ear compared to the full size shure headphone. For me on ear's aren't very comfortable and won't last you very long until your ears hurt, though if you're traveling time is about 45 mins then it is fine. If you are interested in HD 25's, you might want to check out Beyerdynamic T50's which uses the Tesla technology found in their flagship T1's if I'm not wrong. In terms of soundstage, I think the HD25's cannot beat a full-size driver, however, the 25's and the T50 are are definetely inclined towards being more portable. I don't know much about custom one pro, sorry about that, but from what I see it is easy to drive at 16 ohms which perhaps suggest an i pod can drive it by itself. Hope this helps.
Jonathan.