Quote Originally Posted by Lyrica_Ashtine View Post
Except that Fey Illumination isn't a 60 second CD, but a 120 CD and has a 20 second duration. Not considering the effectiveness of the healing for now and assuming you chain cast your heals within the 20 seconds, you'd end up with 9.6 GCDs worth of healing or 1.6 GCD "saved". Whispering Dawn would save you 1 GCD at most, so Eos would be good for 3,6 GCDs/2 minute and assuming you use them whenever they're available.

In practice, however, using Whispering Dawn and Fey Illumination whenever they're up is rarely effective or required. Chances are you'll a good chunk of time on it and you'll spread them over the fight, rather than using them together. While the maximum GCD "saved" with Eos is 4 GCDs (rounded)/2 minutes, you'd need 8 GCDs within the same time frame to patch up for the lack of attack speed buff. Which can be used whenever it is available, unlike healing CDs.
Not really sure I agree with your math, but I appreciate the response =)