I've had two insane pts that are memorable.
1. Had a roaming pt starting at 15rng that went to 33...one pt, non-stop. pt started off as RNG RNG RNG RNG RNG SMN. there was no pulling, we just ran around valkurm/qufim/yhutunga slaughtering things. Along the way people came and went, but 3 of us were there the whole time. We wouldn't even stop for replacements. Some of the newbier people that joined us were overwhelmed and quit ffxi to play WoW or one of those other noob games where they won't have to deal with the stark-raving lunatics. It was rather a unique experience. Basic strategy was for Rngs to stand around the mob in kind of a circle and bounce the hate back and forth...the mobs died so fast we barely took damage. It was especially effective at 24 when we could utsu

2nd large amount of xp i got was a pt from lvl 61 to 64 or 65, I don't remember the exact levels involved, but I do know that I got over 60k xp in one non-stop pt, which at the time was nuts for me.

Now that I've hit 75 and gotten merits and am partying w/ ppl with merits and godly gear, I've surpassed both of those pts as far as total xp just b/c I can get that much xp in a relatively short time. Especially in the new areas. Those pts were marathons that started in the evening and didn't stop until sunrise, so I'll always remember them even though my xp/hour continues to grow.