I think any sewer armor is fine if you do do the roundup in two smaller groups per room. It is also easier on the party if there are lower level players or two bears in the party. You need a lot of aoe firepower to wipe that one big group. I did it yesterday wearing level 51 orange armor with my bear alt and didn't have a problem as long as I timed my buffes and health pots. Just dont taunt an active fire trap and you should be good.

By the way, Tengotengo -- I saw something similar happen yesterday when I did the round up with a party of 51s and 52s. I brought this huge mob back and they proceeded to lay a beat down on the party. Luckily I held most of the agrro while the lone standing pally did some quick res work. MrWallace is right about going small if you don't have a strong party. The roundup isn't for every trip through Stronghold, or so I found out.