Doing some napkin maths it looks to be a slight DPS increase, but I'll have a more conclusive answer once I finish raiding.
Edit: after fiddling with the cloak - in the most optimal way, where we just hit the hit/haste caps, the cloak comes out 3 DPS lower than the current cloak. That being said, I couldn't find a way to get close enough to the caps to make that happen. Looks like the current cloak is better because mastery > haste once we hit the cap, and we don't have as much excess haste as what we would have with Red Sky Cloudcloak on.