At level 53 I did make a trip back to the Noble District to complete the arena quests/challenge in the Armsman's Tavern as well as running the Cistern/Main systems instance and related quests (the entrance is right behind Armsman's Tavern). You can start the arena challenge in your forties, but you have to be 54 to complete the last challenge. That challenge gives you an Epic weapon/shield and you also get many nice blue items on the way to the last challenge. The last 2 challenges require a good group with both a healer and tank in their mid to upper fifties.