Raiding in WoD starts next week, and Sentry has done a great job of recruiting raider to get us past full ranks for 20+ man raids. With normal and Heroics being flexible (and separate lockouts), we should have much for standby if any (we might pull out low DPS on some cases to make bosses easier on flex). Once we start running Mythic though we will be set to a hard 20.
For progression fights (first couple of times killed) in mythic, we are going to take a roster based on what gives up the best chance of downing the boss. That will be determined in several ways, combat logs, don’t stand in shit (people who die less), and stuff like that. In the past we have focused more on total EP, which will still be a factor, but less for mythic. One factor might also Proving Grounds: Gold in your main spec for Mythic priority, so might want to try that out.