for 10-man as long as 7 people in the raid can pull at least 2200 dps you don't need to stack polarity - all DPSers can spread out across the entire back of the room (some on the edge of the platforms for example) and you will kill him just fine before enrage.

For 25 man each person needs to pull 5500 dps so you do need to stack polarity, since 5500 dps is tough unless you are geared in ulduar25.