Having said this, in my research your goal shouldn't be to get as many "good" (.edu .gov) links as possible...Rather, you should be looking for a "natural" pattern.

I believe that a ratio of about 30-50 "average" links per 1 "good" good link is optimal.

IOW, if you have 2 .edu links, you should concentrate on getting (about) 60-100 "normal/average" links.

The same with PR. While it may be tempting to have 50 PR6 links, you're probably better off with a more "natural" mixture.

Linkage patterns are pretty easy to detect and anyone trying to "game" the system will stand out like a sore thumb. It just isn't natural to have 50 PR6 links and none from PR1-5, for example.