All tomes now stay through Reincarnations. So eat any XP or stat tomes you like. I've personally TRed a character since that change, and can confirm they do stay.
I ran Eye's of Stone about 40 times to get my second Maenya's Fist. My first one got eaten by the bank.
Full guild runs are better, especially on elite, because those quests have better drop rates on elite, and we'll will pass what we know you need so long as we don't need it ourselves. Since I'm not farming for that set anymore, except maybe for my Druid (and that's debatable, since she's a test character and not a full one), I can pass anything we get if we run it together.
Not every quest has better drop rates on elite. Most of the older stuff does not matter. I'm not sure when they changed over, I think about the time of Sentinels pack, which was U7 I think.