No idea, but Cree's aren't that expensive and pretty much the led standard for most anything led related (aquariums, flashlights, under-cabinet lights, led lanterns, vehicle lights, etc.) Another thing to consider about led aquarium fixtures is the optics. I don't believe that finnex uses any optics on their fixtures, which may eliminate some tanks from needing 2 or more fixtures for adequate light spread. Quality leds paired with quality optics will produce a nice finished look not only for your fixture, but also for the light penetrating your water column. Optics, depending on the degree of angle, will also help with the "spotlight" effect that cheaper led fixtures (not finnex) produce.
You should post a build thread when you get around to building it. Building my own led fixture has always intrigued me.