It depends... if your site has low or no pr and the backlinks are quality links then it can definitely boost you, but if you already have a high pr it may take more than just a pr4 and pr5 to raise you to the next pr.
nop! if you have only link from one page pr4 and one page pr5 you will get nothing.. but if you get link from site wide from pr4 and pr5 site with more than 1000 page/site, than you're very lucky..!!
myp was correct. if you have PR0, average PR5 + PR4 should get you PR3. however, if your PR is higher then 3, you'll probably won't see the deferent.
i think your site may get pr 3 or pr 4 on next update but it's importan to know how many outgoing links there is on those pages
PR5 is very good. That will help a lot. PR4 is average, though it is muh better than most websites. Many people can reach PR4 with little effort, but PR5 is difficult, so PR5 link, if relevant, counts a lot.