After getting to level 40 NPC, I have been able to predict which fight my NPC will level on. I decide which level mobs to fight based on assuming that NPC is "in" a party with you and that they get exp based on what a duo pt of their level would get on that parcticular mob. For level 30-45, fighting mobs 5+ levels above will give 200 exp per fight, so I've made sure to always fight things at least 5 levels above Cupapa. Second, I believe that the NPCs need the same amount of exp per level that PCs would. Tonight Cupapa leveled on the 33rd fight from level 39 -> 6600 exp, 6700 being the total tnl to level 40. I assume that she had 100+ exp left over from dinging to 39. Even if my assumptions on the duo party exp rate are wrong, it can't hurt at least, I know she would have to be getting at least 200 exp per fight.
Last observation -> uleguerand range is the highest level area that an NPC can get exp in (I think). I predict someday people will seek for NPC leveling pts as the NPCs approach the high 60s/low 70s, since espcially mage job types (no, not you crazy rdms...) would struggle to survive much less make it through 15 fights in any decent amount of time. Also, since I remain a devout pearl dropper even after the update, I can vouch that it doesn't effect their exp. My NPC is attacker, idk if that would unlock headgear option or if that's healer type only, but I haven't noticed any new options in a while, suggesting that pearl dropping causes backslides in that aspect of NPC upgrading. Also, her gear was improving improving... looked like full Noct. gear (awesomeness!) and then today she randomly decided to pull out the scale mail -.- So I don't think dropping pearl affects gear... she seems to spite me whenever I get excited about what she's wearing ;;