There are some mysteries which are so deep, that men can never fathom the dephths of their meaning. I have realised, that the Fourth mode is one of these mysteries.
Seriously, I've been chanting the office regularly for about three three years now, and yet the fourth mode confuses me. IT FAILS TO MAKE SENSE. I'll start off with an antiphon or responsory or hymn or something, and the whole thing will sound EXACTLY like the the first mode, and then, whoops, last note is different. That's where I was with they hymn Decora Lux last evening. It sounds and appears to be in first mode, and then the last note is different, so it turns out it's not. That makes learning it a bit harder. Sometime I wonder if the fourth mode is actually just a very successful trolling attempt that no one has figured out yet.
And also, everything they say is true: Pius XII/Bea psalter= COMPLETELY UNSINGABLE. Don't waste your time. Stick to the Vulgata or Nova Vulgata.The phrases are far too long for me personally. It seems like your stuck on the dominant for ever. Sometimes they're far too short, and you're on the dominant for a single syllable before going into the termination.
I'm still on the fence about whether the Nova Vulgata is better of the New Nova Vulgata. (Yup, they revised it. The revised version is in Lauds and Vespers, but I have he older version now. The only real differences are in the canticles.)