Google use new technology for PageRank. I think you cant' prediction about Google PageRank for the future.
Pagerank Prediction is not always right. However, you can check them at link.ezer.com or iwebtools.com
There are too many modifications to the PR algorithym, I mean all the search engines are forever tweaking their algorithyms to ensure optimum results, so keeping up with PR is a task in itself, i wouldn't rely on prediction tools that become obselete in a short space of time