Having previously owned the SE535-J, my answer to your questions are as follows:
1. Yes, the 846 took what was a great midrange and polite treble and added a visceral bass. The way I describe the 535 now is a beautiful house without a basement. The 846 added the basement. Further, the clarity, instrument separation and balance were all improved. Finally, with the replaceable filters you can turn the sonic signature to your tastes.
2. I agree with Revolutionz, even though they are larger and heavier than the 535, the 846 is actually more comfortable. It must be the overall shape or weight distribution.
3. The treble is about the same as the 535-J which has the extended treble but it is very polite and not fatiguing.
4. I cannot comment on the stock cables as I think I listened to them for about 30 minutes before switching to an OCC silver cable from Headphone Lounge that I used on my 535.
5. Same as #4 above.
One word of caution I agree with is from Arnaud on the other SE846 thread http://www.head-fi.org/t/663180/shure-se846-a-new-in-ear-flagship-from-shure-finally-impressions-p26-28/2175#post_9834325. With an input impedance of 9ohm, the choice of DAP, DAC and/or amplifier can be important.