I'll give you first hand experience.
I have run Ushio 14 K for 2 bulb changes.
And recently have run Phoenix 14 K.
Coral grows much slower under the very blue phoenix bulbs.
I plan to go back to Ushio 14K when I order tomorrow.
Do you have a year to wait for my results?
I'll be waiting for results! I'd have to also ask though, which corals? Saying "corals" implies all of your corals, is this true?
Also, to bring up one important point, corals don't use light, their symbiont do. They then get energy in the form of organic carbon from the symbiont. They still need other nutrients to use this carbon (for example see Falkowski et al. 1984)
"Light and bioenergetics of a symbiotic coral. Bioscience".
Also, zooxanthellae can only use a certain amount of light, perhaps less than one might expect (for example see:
http://www.advancedaquarist.com/2007/3/aafeature1).
A recent review article Osinga et al. (2011) "The Biology and Economics of Coral Growth" lists 4 reasons corals may grow slow as a result of light.
"1) insufficient production of photosynthates"
"2) insufficient
translocation of photosynthates, for example after enrichment
of seawater with inorganic nutrients"
"3)a decrease of the internal pH due to lower photosynthesis,
leading to less favorable conditions for calcification"
4) photoinibition
Of the 4, #2, as mentioned deals with insuficient food/nutrients to use the light. And #4, deals with too much light. #3 could be a result of too little light, but could be other factors, such as bleaching for example. #1 deals with too little light.
So, just because a light is or isn't more photosynthetically productive, doesn't mean it will necessarily effect growth of the coral. For example, I could hypothesize that if a lamp radiates too much usable light, the coral may photoinhibit and growth could decline. If I then switch to a lamp that uses the same power, but radiates more light in less-usable wavelengths, perhapse growth will increase, because the coral will no longer be photoinhibited. This doesn't say that one light is better than the other, but rather that there was too much light with one. Perhaps, in this case, the same results could be obtained by reducing the intensity of the first light...