Ed,
Here are a few facts / numbers from my expierence from switching to led's. First off I like to have the ability of being able to adjust the colors seperately. I have white, blue, and royal blue led's, my former fixture had 2 150w 20k MH and 2 130w dual attinic PC color and growth were ok for years.
I monitored the amperage usage over the past couple month, and what I save in electricity for the lights is about 200.00 per year. This does not include the 4 to 5 times per lighting cycle the chiller and pump would run when the MH were on.
Yearly cost of changing out the MH and PC was 200.00 per year. If you can belive the led manufactures claim of 50,000 hours of use at 10 hours a day that is 13.6 years. Between the savings in electricity and the saving of yearly bulb cost the fixture should be saving about 4200.00 over the life of the fixture.
I am not going to tell you the my coral growth rate has doubled since switching or any thing like that, but all corals are doing good. The only corals that has some improved growth rate are my sps.
IMHO, Both MH and leds are good for keeping a reef tank, but when you run the numbers and having the flexibility of led's its not hard to see why there are alot of people switching over.
Hope that helps.
Mark