Imagine for PR4 directory. There will be possibly PR1 or PR0 on the inner links. Nonethless, it is always beneficial submitting to high PR directories. Today may be PR2 and tomorrow it could jump to PR4 on the inner pages.
Search engine only consider page, where link is put. In short link Page PR only support your website.
PR7 directory definately has some authority.with the title and description thats there on the category will definite benefit in SERPS