We use tiers (or their functional equal) for feats on our wiki, so you may have a head start there. While doing all the feats ever would be a difficult task, doing them one at a time is reasonable. As a general rule, Core never really goes too far above our Moderate, which I think equals somewhere around the 3-4 range for your system. With a few exceptions. Of course, things would be generalized of course.
I would recommend an "unquantifiable" tier, Leadership really exemplifies that.
As a slight sidetracking, I've recently enjoyed the concept of a tier system more akin to alignment; two scales measuring both its overall power and usefulness, and its versitility. Because there's a lot of feats (and classes) that are really good, but one trick ponies (uberchargers), or really versitile but not too powerful, or both (wizards) or neither (CW samurai), and it just seems more... descriptive.