That ones beyond me, so far....
Although the dual pendants is a good start. The other thing to keep in mind is your tank depth. If it's a shallow tank like mine(12" deep) you might not need that many. Also your optics , if you use any, can make a big difference as well.
The next led build I'll be working on, is going to be using 90degree to 120degree optics just cause it's so shallow. Although I think most people use 40 to 80degree optics. And again you have to research which ones are best to use.
if your going the diy route, try and find some UV
led chips for better penetration.
Also to get even more light outta of your fixture look into 3-up Indus stars that have 3, 3watt crees mounted to the chips.
Though I have to say that having a dimming option is a must have for any fixture. Which is why I like the trc drivers, there pre-wired to accept a dimmer. With out the hassle and added cost some of the other drivers have. My sliding dimmer only cost 4-5 bucks or so, without an additional power supply or fancy controller. Just soldered the wires up and it was good to go. I love simplicity. You should try to make it out to the Ann arbor swap tomorrow if you can. Lots of people will have led fixtures there in use, some diy and some store bought fixtures.