Should I buy a site-wide text link from a PageRank of 8/10

From my personal experience the only problem with buying site wide links is that Google tends to filter your site for the anchor text unless you have a trusted domain.

So if you got site bound links with the anchor text "Free Ebook" then you can be pretty sure that you won't show up anywhere for the keywords Free Ebook in Google. Msn and Yahoo on the other hand seem to like tons of links with the same anchor text.

I think it probably has something to do with the diversity of anchor text, it doesn't seem to hurt your sites ability to rank for other keywords tho.

 

an interesting observation - so you mean to say that though you risk your rankings for that keyphrase with google, it only effects that keyphrase and all the other keywords you are ranking for should be fine