In Game Development Team we have several unique specialists which can not do job of each other: Artists can't programm, Programmers do not know how to create 3D models, Level Designers can't do both of previous (will call them subteams). When planing, XP says: "Write user stories, asign them into iterrations according there business value limiting by team velocity." The problem is that is not clear how to plan stories in particula iterration because we need to balance job between different subteams .

To solve this problem, as I see, it is need to consider personal speed of every subteam when planning or separate project into several subprojects.