LAST EDITED ON Jan-08-07 AT 00:27AM (MST)[p]The EL is lighter than the SLC and feels great in the hands, but to my eyes, they're not worth the difference in price, and I've owned both. Maybe a small point, but I also prefer the armoring of the SLC to that of the EL because the biggest portion of the front of the EL's is painted and easily dinged and scratched. Doesn't affect their function of course, but they can end up looking like hell in a hurry.
Maybe not the best description, but diopter compensation refers to the range of the eyepiece that focuses separately from the center focus wheel, meaning you set the diopter adjustment to one eye, and the center focus adjusts mainly for the other eye, so they both have a clear view.
If I'm not mistaken, interpupilary distance means how wide they'll open and close on the center hinge to fit an individuals eyes/facial structure because everyone's eyes are different distances apart.
Don't know if you're aware of it or not, but Swarovski just had a significant price increase (I've heard 10% across the board, but don't know for sure?..) on 1-1-07, so if you plan on buying in the next little while, I'd try to find someone who might have some "old stock" and honor last year's price, but I wouldn't wait too long.
Doug @ Cameraland is the man when it comes to optics, so that's where I'd start.