First off, DSN has better luming on his. This would usually cost around $120 extra if you later decide to get a non-DSN watch lumed.
As well, I believe DSN uses a slightly different case design, but this would only be a problem if you intend to put a Swiss 7750 into it. Also a different crystal and cyclops, DSN crystal is composed of two wafers put together, top one being Sapphire, not sure about the inner/bottom one. The font is also different on the date wheels, I believe that the Ultimate is thicker and more accurate in that regard.
There may be other differences as well, but I'm not sure.