I was wondering if anyone could tell me whether a link from an industry related site with a pr3 is more or less valuable than a link from an unrelated site with a pr5. Hope that question makes sense
Yes. Vanessa Fox, Product Manager of Google Sitemaps says so. >> As a "Quality" Indicator - PR is way Over-Hyped Cryo.
Stay relevant. Don't link to sites outside your theme. It doesn't matter if they link to you, just don't link back...it's a waste of time.
I'll go for PR3 as it is relevant with your site and that is one of the most important thing to consider when linking with other sites...