First, let me say that sites do not have PR. PageRank is assigned to individual pages, not sites.
Second, you aren’t going to get a PR5 page from a single PR6 Link. You will need links from several different PR6 pages at least.
And Finally, let me say that the outbound link juice is divided by the number of outbound links. so if there are 2 outbound links from a page only 50% of the link juice is passed in each link. If there are 10 outbound links then only 10% of the link juice is passed to each outbound link, and so on.