Found it on pages 337-9. I believe that's intended to mean all the Attributes combined. Personally, that doesn't make sense to me, because a baseline human should have 4s in everything except EDG (which should be 1). 10-15 points below that would be a severely restricted character. It seems to reflect an assumption that most PCs will have multiple extreme Attributes. That's not been my experience. Aside from Module, Field, Trait, or SPA prerequisites, there's little reason to take something above 4. I mean, a 7 will get you a +1 on a wide swath of skills, but how many of them do you intend to use regularly? In general, you're better off just buying the skills up. If you have a lot of skills, Fast Learner is usually a better investment for 300 XP.