I agree that you'll look very smart in the white shirt, black tie, and argyle jacket w/ waistcoat. I went to my senior prom in a kilt and PC get-up (quite formal, as my high school has lots of wealthy families who do this stuff with each other a lot). Here's the photo:



Obviously over the top for a standard prom, but at mine (held at the Los Angeles Convention Center, no less!) it was fairly standard in terms of formality.