1. The calculations are for mana efficiency only, and ignoring burst completely. Since we can use all our mana in a case where we actually have stuff to heal with it, haste doesn't play part in this calculation at all.
2. You probably entered some wierd parameters, because even for pure efficiency deathchill looks a bit better with my numbers. I wouldn't spend the gold on it since it's inferior to quite a lot of other cloaks that are much easier to obtain. If you want a crafted one for similar cost,
[Pattern: Wispcloak] is much much better.
At the end, keep in mind that SP/haste matter more than their efficiency value. How much more depends on how much you need to "do more healing
during the whole fight" vs how much you need to "do more healing right now", and how much stats actually help you do that.