I think (my personal opinion) is that high PR sites, when off topic, do not help at all.
Why?
Because I purchased a PR6, 2 PR7, 1 PR8 for one of my 2 sites listed below (PW). I didn’t purchase ANY links for PSW (other site).
PSW = PR4 (no purchased high PR links)
PW = PR3 (purchased PR6,7,8 )
I’ve heard that Google has devalued these high PR off topics – and this just proved it to me. I no longer purchase links for off topic sites.