I would be cautious about thinking ED gives one a boost by looking at ED rates. Penn very clearly states that the ONLY time it will consider legacy admits is during ED. They are also very clear they admit over 40% of their legacy applicants. (http://thepenngazette.com/five-is-four-cs-%E2%80%A8and-the-right-road-to-college/ - this is actually a very good general article for college applicants and their parents. I found it very helpful beyond the legacy issue)