you can not really predict the PR. who know that the high PR site you get link from will get PR dropped or upped or not. just build link as much as you can and wait for the result.
Hey there, Even if you knew the pagerank equation, you could not figure it out unless you had a snapshot of the google database for a given point in time. You would have to know every single URL pointing to your site, the number of outlinks on those pages, the quality of those pages, etc.... Sincerely, Travis Walters
All PR prediction tool are fake and nobody can do PR Predication. But you can check your PR on diffrent datacenter of Google through this tool : http://www.seologs.com/pr-check/pagerank-dc.html
Basically, no one can predict PR. It is because search engines like google have to update their algos every now and then. It means that the you could not predict your pr. Unless, you are an employee on all of those search engines out there. hehe
You don't have to predict it just optimize your site proper a relevance link is a big help to earn your site PR.