There's no way a progression guild would get far into Tier 6 content using a 5-box team as a main raiding staple. I could see it being viable on many things, but not T6 bosses. On Teron, ghosts overlap a bit, what do you do when more than one of your characters is a ghost at the same time in a different spot, and the others are all still trying to DPS? It'd be a disaster. What do you do on Supremus when one of them gets punted away and the others are standing around potentially in a volcano? What do you do on Archi when someone is thrown into the air? What do you do on Azgalor when one of the toons gets doom and the others don't; can you run him over to the tank while the others maintain DPS and stay out of fire? What about Bloodboil, maybe he's at 30% and group 1 and 2 need replacements for bloodboil soaking at different times? Then the groups all spread out for phase 2, what happens?

Even if you found solutions for some bosses, it's not practical to expect to raid and get anywhere far. 1/9 BT is not a great feat, no offense to anyone. Najentus isn't the problem.