XP / SCRUM有多大？

In the earliest stages of planning the development of a new system, which development model to follow seems paramount. I've always held onto the belief that a classic waterfall (or hybrid waterfall/iterative prototyping) is the best approach for medium to large projects. It seems that once a project gets to be a certain size, the Agile/XP/Scrum paradigms can't account for complex requirements, a large team, the complexities between multiple sub-systems, the need for documentation, personnel changes, etc, etc.In the earliest stages of planning the developm