According to Cree's data sheets, Royal blue runs 450-465 nm wavelength while the blue (or cool blue) runs 465-485nm. I'm not sure how much of a difference you'll see by the naked eye. The question comes down to what your research shows is necessary for good colour and coral health.
This is where I believe DIY full spectrum builds differentiate themselves from stock fixtures and what will ultimately drive where high end fixtures will go. But for now, these full spectrum builds are just experimental and we'll see what grows things the best...