I seriously doubt that I will get PR10 – all they base it on is the backlinks (number + PR). If I do – more for me, but I dont expect more than PR7, in my wildest dreams – PR8.
The best way I have found out to check your future PR is by adding Sitemaps to your site.
Google does divide the pagerank into four cats:
a) Low
b) Medium
c) High
d) Not assigned
Low is from PR0 to PR3
and I know medium is from PR4 to at least PR6 – I have no way to validate the last figure, since I dont have PR7 to compare, but I should know more after the next update 
Anyhow, it seems that Google will assign PR on the Sitemaps, without showing it on the toolbar, so you can always see if your pages are in any of the four parameters above. If you have a green on Medium for all your pages, you would not know if they’d be PR4 or PR6, but it’s all in the same category anyways.
Hope it helped.