Our AoE dmg is being ranked higher and higher as we're getting gear. Both dots and Mindsear are granted huge benefit from haste and mastery.
I am using spells in this order:
2-3 targets ... standart rotation with multi dot.
4-5 targets ... dots and mindsear as filler
6 and more just Mind Sear.
Also last tier talents are focused on AoE, usually used on cd.
Without t14 or t15 set bonus it may be better to start Mindsearing at 5 targets.