I have always used a paid VPN on torrents site and never been ban or asked not to use it. At the end of the day I would rather put my faith in my own hands then to hope any tracker site public or private puts my privacy first. Also people do get letters from their ISP on private torrent sites, I have seen people mention it at Torrent Leech and Torrent Day. In the end it really is just the luck of the draw on getting caught.