Page Rank and Search Engine Result Ranks are completely different things and have nothing to do with each other. Page Rank only depends upon the backlinks you have pointing towards ur site. The powerul links you have, the higher will be your page rank. Where as Search Engine Ranks depends upon the quality or relevance of links you have, originality and uniqueness of content and many other factors. Google looks over 200 factors to rank web pages in its results.
Then why do people look only at PR of the link, when you propose to exchange links? It is just a page rank that only google needs, isn't the main the position your site occupies in SERP?