If you look at a linking profile of a naturally linked website, you will notice that links from higher PR sites are less than those that are coming from lower PR sites.

It would be unnatural if all your links are coming from PR5 and above pages only. The bulk of your links in order for it to look natural must be from PR0 to PR3, then as you go up, you should have less and less links.

In my opinion not more than 15-20% of your backlinks to a site should be from PR 5+ pages.

The more natural looking your links are, the better it will rank.