PR means nothing in terms of ranking. PR is pushed to the Google Toolbar once every 3-4 months, but changes in real time all the time. Even if what you saw was pushed weekly, it'd still be out of date.
What you should be worrying about is their optimization, not the PR. Even Google says you shouldn't care about it. They've even wanted to remove it it in the past to stop people like you from making assumptions, but decided to leave it as a general indicator of a page's worth.
Again, exact match domains are nice, but aren't the end-all-be-all for ranking a site. Otherwise, sites like "Dogpile" wouldn't rank for terms like "search engine". If you search "search engine" in Google, you'll notice that only one domain there has the words "search engine".
You need to analyze the competition and figure out what makes them tick to get a strategy for how you'll enter the niche. An exact match domain name is only a fraction of that strategy.