Perhaps a dog-tag system like in Bad Company 2. If you kill someone, you get their dog-tags (or wings, but the specific item is irrelevant), which you would keep in the O'Club. You would not get multiple dog tags for killing someone multiple times, just one dog-tag per person. If you clicked on the dog-tag, it would bring up a little card with infomation about the date, time, location, arena, respective planes, weapons used, and the damage dealt to you and the other player. An algorithm would calculate this, and create a score; the color of the dogtag would vary based on this score (i.e. Bronze, Silver, Gold, Platinum), and one could see it if one were to click on the dogtag.
-Penguin