I custom built a CREE system like you are describing and although I ordered a whole variety of optics, none of them work on my tank. The water is 14" deep, and I believe you really have to get over 20" to have the 40 degrees as a requirement for deeper penetration.
Since your tank is quite long you may want to utilize some 80 or 60 degree optics for spreading the light out, or use a lot of LEDs.
I would recommend Nano-reef for learning how to build the system. Evil has many posts there and the documentation is excellent.
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