My guild isn't the best, but we're 9/13M. But it just takes so long to go through farm content.. At least for my guild it does. It could take us anywhere from 1 to 2 nights of our raid to kill farm.. Whether it be because we for some reason get stuck on a boss we already killed or we are just not fast enough killing farm content. That leaves us with 1 night to do new things, unless we save the lockout.. Which then people who need loot from earlier bosses are shit out of luck that week.
I think an 8 to 10 boss instance is a good number. If Blizzard is too worried about people clearing it way too fast, then why not just make the fights harder?