Just something to consider. LEDs spaced 2" might look like a row of flashlights, even with wide optics such as those. I haven't tried that spacing or anything over 60 degree optics, but that's a lot of room between them if the fixture will be near the water's surface. It'll also depend on mounting height above the tank. You could always PM evilc66 and get his input, too. He's the man and has helped a ton of people to plan and troubleshoot their layout.
I haven't seen Powerbrites in person, but these will be much more intense if driven at 700mA or 1A. According to Marinedepot, the Powerbrites are run at only 350mA, and it's likely that they are using older, less efficient LEDs. I looked into getting a unit when they first came out, but the fact that they are only driven at 350mA killed the idea for me. Without a doubt, a CREE XR-E setup driven at 700-1000mA will outclass the Powerbrite.