just want to point out, if you run CREE on a 20g tank, you probly won't even get to 50-70% intensity, you probly just going to run around 30-40 depends on how deep your tank is. I know many people running CREE fixtures at 80% or less for their 24" to 36" tall tank. I think it is better to go with a bit more spread out DIY build with a larger degree lense, so that you can turn up the intensity a bit more and still be able to cover whole tank.
to be honest, the cree vs bridgelux question is really depend on certain situation.
the both are great LED chips and both deliver good spectrum when give the right combination. People get down to detail about how much energy that someone gonna save by using CREE vs bridgelux in a long run. While that argument stand very true, but what about those people still running 2 or 3x 250W MH? It is the same argument when comes to people why they choose to use MH instead of LED, front end cost? proven technology? I would consider bridgelux to be a stepping stone for someone switching from MH/T5 to LEDs, and CREE would be a advance version of it but not the best. I would always consider Luxeon ES LED the better brand of the two and DYI can be found at
http://stevesleds.com/.
Usually for a smaller tank, the cost differences are really small, it is only when you start to DYI a fixture that need to cover a larger area like 48x30 or even larger, the cost differences will stand out.
PS: I also copied a comment from 3reef and I think it is very true as well and should be consider when doing DIY, as DIY should allow you to make mix and match on LEDs and shouldn't only stay with just 1 brand of LED. "Bridgelux diodes have much better spectrums available, like violets, deep reds, cyans, etc. but are less efficient, usually about 30% less efficient. They also have lower current and voltage than Crees, but are much cheaper, making them the more affordable option in most cases. The best type of fixture would be a hybrid, royal blue and cool white crees, and violet, red, green, and cyan bridgelux diode. "