do a search online. CREE vs 5mm LED, or even the 10mm LEDs. They dont lost a long time. CREE as far as I'm aware, which has been proven by their older models, last a long time, longer than 5mm or even 10mm.
The LED unit that i build is comparable to the Orphek LEDs that some of you may have heard about. They sell one unit for 900, i sell mine for (when people want me to) 500, depending on what they want. But they pack in 60 LEDs and i do 28. Theirs is designed for deep tanks, 48", mine are for 36" but are adjustable depending on the depth of the tank.
The 5mm LEDs, to me, are for those who want to save money without spending a lot, but that has it's drawbacks. I would warrant mine labor free for 5 years and the PSU for 2. In a retail store, i bet these would sell for 7-800 each.
The power savings of LEDs over 5 years pays for itself compared to MH. No bulb replacements, 50%+ less power consumption, less heat so no need for chillers, but to each their own ya know. Weather you go with 5mm, CREE, MH, PC, etc, its all choice on what you want/plan on doing/need for your tank. I went with CREE because for a couple extra hundred, i have a very versatile setup that i can do whatever, and if future proofing is considered a luxury, thats what i would rather have. Upgrading isnt cheap, esp if you consider how much you lost on selling your used equipment.
Look all over the net, there are tons of articles. LEDs dont provide the broad spectrum that MH or PC's do but they do supply what is needed.
Check out RC, they have a TON of info on it. There are many factors to consider when buying lights, dont short yourself or you will pay for it in the long run.