Jeff,
Do you feel the DIY cree LEDs are equally as good as your Prometheus LEDs? If not, what do you think the differences are?
I cannot accurately respond to your question, I have not used a DIY cree LED system yet.
The biggest differences are:
Controllability; sunset, sunrise, cloud, thunderstorm, moonphase, controllability to each led to spotlight the exact corals that need more light and to dim the exact spots where corals need less light. You can also adjust the Blues, Royal Blues, and White all separately to create the color temperature that is needed which is HUGE when it comes to LEDs. You don't want to be bleaching your corals. Not to mention, you can control these lights with your iPhone or laptop wirelessly using wifi or bluetooth, or with an usb cable.
Cooling; I have yet to see the prometheus operating temperature go past 55 degrees, even running in 80 degree room temperature running at full 100%. FWIW the temperature probe is mounted between the heat sink and the led boards. The 2 quiet fans automatically ramp up or down to keep the unit running cool. Keeping these LEDs cool are KEY to the life of the LEDs.
There are more differences but i'm sure you can go onto their site ReefTechLED.com for more information. I don't want to sound like a salesman too much as this is not the point of the thread. All I can say is, in my honest opinion the prometheus is worth its cost pound per pound, this light is half computer and half LED. Thus, why we chose ReefTech and will be converting the whole store over with ReefTech LEDs whenever there is left over budget.