The amount of trickle down from the PR of other pages has never been revealed, and has changed in its importance to SEO in general over the years. It is true that you want high PR sites to link to yours, but the importance of social interaction has not only contributed to results ranking, but has been eluded to by G to have influence on PR as well.
I wish there was a simple formula, but I would not suggest going with a high PR only linking campaign. The secret to importance, ranking, and popularity of content's percieved quality in general has overwhelmingly become a matter of a mix of diversity and relavence. Go for high quality BLs period. The PR ranking will just be what it is. If you are doing "right" it will go up, but I would see it closer to domain age than ranking position, as it less likely to be influenced by you than by G internal whim.