So banded is great: it's cheap enough that you can use your leveling plat to buy it and it adds AC, which works for you the whole fight (unlike extra max HP/Mana). The problem is finding a banded seller, as most blacksmiths now have too much money to be bothered to sell banded.
So what you're weighing is:
- how much XP you'll lose in the time it takes to run to EC, wait in the tunnel until you find a banded seller, then run back
vs.
- how much XP you'll gain as a result of wearing your spiffy new armor instead of gnoll scraps
For the sake of argument let's say banded saves you 2% HP vs gnoll scraps, making you rest less and earn 2% more XP
per level. Over the course of 30 levels that adds up to (again, with rough math) 60% of a level.
Since it's hard to say how long you'll be waiting in EC it's hard to say whether you could have earned more XP just sticking to you current hunting spot wearing gnoll scraps. I don't think there's a clear right answer here. Since neither way will be obviously better, I'd say run to EC if you're tired of leveling and want a break, or stay where you are if you're happy leveling.
If you do go, try and make sure you have enough plat first so you only have to make one trip. If possible, use the EC tunnel forum here to find a vendor first, so you don't waste hours sitting (in-game) in the EC tunnel. And if you have any extra money consider grabbing a piece of totemic or jaundiced bone armor; sometimes they can be very affordable and offer much better AC than banded.