Neither, keep the iPhone 4. Save your money for something better than the E7 or J3 if you decide you want to upgrade.
Figured out the mid's issue w/ the CKM500 for me. After A/B w/ the MDs they have better clarity and apparent detail as a result in mid/upper mids. The problem w/ the vocals is the CKM500 sounds like it has a severe recess in the lower mids which takes the weight and heft out of the vocals which is why they sound a bit thinner and delicate. This translates as vocals sounding like they are always coming from the lips and mouth without air coming from the throat and diaphragm. This is where phones w/ more complete midrange provide a fuller, richer harmonic to vocals and other stuff living in the same area. You can get a sense of air rising from within and passing out in a cohesive fashion. To illustrate, listening to Lionel Richie's 'Stuck on You' one can hear it clearly when he tries to say the word 'home' at the end of the phrase at 1:10. The word 'home' just drops off a cliff which is the same area where lower mid harmonics would be building up the rest of the vocals. For me it's the difference between actually singing and mouthing lyrics.
In the end, the CKM500 has clear detailed mids, but at a cost which makes me find them somewhat incomplete but certainly delivers a 'wow' factor upon first listen. The bass is also more mid bassier than the MDs which reach deeper and hit harder.
I like the CKM500 a lot, especially for $70+ and the specific reasons I got them. They'll have to tide me over till the IE800 comes out and when I'm not using my ES5 or UERM.
Edited by Anaxilus - 6/14/12 at 2:21am