The real problem is that taking a pair of prisms is two of your very valuable heavy support slots. The Eldar codex really makes you choose what you take now, and when you've got stuff like War Walkers and the Wraithlord that play a very important part in the army, it's a tough call to make. I'd personally leave the tank busting duty to war walkers armed for tank hunting, fire dragons, and a wraithlord armed with a bright lance, and take a squad of Dark Reapers for the third heavy slot, but I've always been quite partial to the Aspect Warriors.
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