I can not comment on the custom sleeves but the Shure Olives definitely sound different than the tri-flange tips and also my new Earplug store tips.
The Olives, remove a bit of the treble and the midrange making the sound warmer and adding slightly to the bass at the expense of not so quite as crisp highs or detail.
From what I have read a proper fitted ACS tips should add comfort, and better isolation which should make them even more detailed and possibly more crisp, but it should also give you the most bass as well. So everything should be ever so slightly better.
Oh and you asked about loosing weight. I am not an expert but I imagine you would have to have a much larger weight loss to have the fat content in your ears change enough make that much difference. But again I am not an expert on this so you might want to wait for more responses in this area.
Edited by dweaver - 12/29/11 at 11:35pm