It depends on the event, and popularity. UFC is usually found on BT Sports 1 and 2, and the UFC channel (in Spanish). It's generally not hard to find a UFC PPV in other places as well on free add-ons, but those usually aren't very good. PPVs are sometimes shown on 455, but usually a clone of the original stream. If it is a big boxing event, sometimes the server guys activate 456 as well.
Some people will get freezes, and buffering, and its kind of up to you to minimize it with a good connection, meaning decent bandwidth and possibly using a VPN to reduce blocking in the routing chain. There are no guarantees on getting great quality at high resolution.
