At peak times you might have a 10 min queue, but that's about it.
There's no CUK guild per se, but there's a guild made up of the old CUK guild, and a couple of smaller guilds who've merged with us (can't remember exact numbers off the top of my head, but we've got enough active highbies to do MC/onxyia etc). You'd have to trial, since there're non-CUK people involved in running it, but I'm sure you'll be fine.
If you do a /who Peacebreakers (don't blame me, was Nightwing's idea for a name >.<), then there should be someone online to throw you an invite.