I have been reviewing the page rank of myself and my competitors. And it appears that PR5 is the maximum across the board. Could it be that because our target market is so small, that being a PR5 is better than mediocre?
I've done lots of optimizing and many pages come up in the top 3 on keyword searches, usually ahead of my competitors. But no matter what, PR5 and I are a pair.
I tend to relate the "expected PR" of a site with the categories its in at DMOZ and Yahoo. If you can situate yourself in one of the top tier categories (one thats relevant of course:) ) then you can get the high PR you want.
If its something like >Regional > Outer Mongolia > Rare Widgets
Then in the scheme of things in the world you would hope that PR is lower.