Re: Mastery [3.5e, Learned Caster Feats, PEACH!]
I can't speak for the Erudite feats, because my familiarity with psionics is lackluster.
Prayer Mastery and Elemental Spell Mastery seem like useful additions for the Archivist and Wu Jen. I profess, though, that I don't think many people are going to use it, given that I haven't seen it used often except as a prerequisite for something else. Might just be me, though.
Master Scriber seems like a standard feat. Nothing wrong with it.
I have to agree with Joshua Z about Master Archivist, though. That feat can get overpowered easily. I think taking out the ability to get a spell that isn't on the Cleric list would help to balance it. Likewise, you could instead include a reasonable rate of failure. Maybe a Spellcraft check?
... Sense of nostalgia, from rereading old games...
Roc Ness Arrgh I forgot there was a 5th gen and that number is taken now. D:
Avvie by Serpentine.