Do I have a high PR 6 or a low PR 6? How many times have you seen a post like this in a forum or have been asked this over the telephone? Over at SEO Chat there is a post that just got started that discusses this exact topic, fractional pagerank.
DigitalPoint suggests that by looking at your inner pages PR, you can somewhat determine if you have a high PR or a low PR. For example, if your pagerank is currently a 6 and your main four inner pages are a pagerank of 5 then it is safe to bet that your homepage's PR 6 is a low PR 6. However , PR (as DigitalPoint knows) not always works this way. If you have any incoming external links to those sub pages from a high PR page, then this might not be true.
For a page that has not had a large number of increased incoming external links over the past months you can determine if you have a high or low pagerank by watching your PR changes over the PR updates. For example, I know my main corporate site, www.rustybrick.com, fluctuates between a PR 6 and PR 5. It has been doing so for over a year now. So I am pretty sure that the index page has a high PR 5 and a low PR 6.