Another quest was found that raised the npc level cap to 55.
http://ffxi.allakhazam.com/forum.html?forum=10&mid=112923086316188700#112927314548644266
I wrote up a brief walkthrough, based on the Angelica route. It seems very similar to the Umberto route described in the other message.
Picture Perfect
Start: Diederik in Selbina, near water
Choose to speak with either:
Umberto in Bastok Markets (L-10, near music store)
or
Angelica in Windurst waters (2nd floor of the inn on north map)
Angelica route:
Angelica will ask you to retrieve a Bal Shell from Korroloka Tunnel. Use a pickaxe on an excavation point to get rare/ex Bal Shell. Give Bal Shell to Angelica, she will ask you to go to Castle Oztroja to get opalescent stone.
Make your way to the stairs at J-8, beyond the trap door.
Head to I-9 and continue east to the courtyard.
Continue east to a Brass Door at I-8, get cutscene at door.
Inspect door again to go through. Inspect ??? to spawn NM Yagudo Muralist, easily defeated by 75 whm and 50 npc. Your NPC is automatically called for this quest, even if you've recently summoned them.
Talk to your NPC, then inspect ??? to obtain Opalescent stone.
Return to Angelica. Go to Bastok and speak with Umberto to finish the quest.
Reward: "Your adventuring fellow's level limit is now 55."
Title obtained: Team Player