I am applying to Wharton ED this fall. For the "movable" supplement, it says 300-500 words. Currently, mine is about 663 words. I tried cutting it down to about 550, but the essay loses much of its humor and does not read as well.
Generally speaking, an essay without a strict cutoff should not exceed more than 10% of the max allowed. So 550 words isn't that bad since it would be hard to notice or tell, but 663 words will be noticeably long .
^I'm assuming you're talking about the 'Why Penn' prompt. This year's prompt is brand new. Their 'experimental' prompt. What they want, what they expect, what they'd like--those standards might've changed. Nobody knows, so I think it's better to play a little safer.
@BusinessBeast: fellow Wharton ED applicant here. I cut my essay down from about 1,000 to just under 500 words. It's possible. It's hard as hell, incredibly frustrating, and almost upsetting but possible. If you'd like I can review your essay and offer suggestions on where to cut/replace.