I've always steered clear of PN due to slowdowns I used to read about,
I was of the same mind with PN and with VirginMedia, but I was then a customer of PN for 6 years, without a single slowdown. Max's issues are interesting and could be local congestion connecting the exchange back to the backhaul, so would affect all BTw ISPs and hence would be fixed pretty quickly.
VM used to throttle based on usage, but that stopped a few years ago.
21 years of broadband connectivity since 1999 trial - Live BQM