<p>I don’t have an incredible store of special knowledge about this, but my strong, strong guess is that – limiting myself to the question you asked – Oxford in general would be a huge, huge plus at U.S. grad schools. There is a lingering crush on Oxbridge throughout the upper reaches of U.S. academia.</p>
<p>Now, it might matter a good deal who your tutors were, and what you actually did. Apart from the strength of Oxford’s Classics program, you are almost guaranteed to have done more impressive work there simply because you will have done more of it, and less of everything else.</p>
<p>The question you really want to ask is what others have been discussing here: Do you really want to give up the breadth and happiness of an Ivy-model undergraduate experience for the marginal leg-up on grad school admissions Oxford may give you? After all, top Classics students from U.S. colleges get into great grad programs, too. If you go to Penn, and work as hard and focus as much as you would at Oxford, and cultivate relationships with the faculty, you will probably wind up in the same (or equivalent) grad program that you would have been in coming from Oxford.</p>