The Behringer product is not a bad product but its no even in the same class as the EV or JBL lines, build quality, component quality, and sound quality are far better in both the EV and JBL.
For your application don't concern yourself with how many ohms each of these are, it doesn't matter.
The JBL PRX618s-xlf goes lower and is louder and is nearly 10 lb's lighter then the Behringer, its a proven performer that is only bested by much more expensive subs. I've owned four of these are they are beasts.
The EV line is also louder and lighter though it doesn't go as low, however I'm going to go out on a limb and say that under real world testing the Behringer and EV are going to get to about the same frequency. This EV line is also comes highly recommended on the Pro DJ Market and the Pro Audio Markets.
As for a forum to check out head on over the Pro-Sound Web, they have a great forum with a bunch of great guys that do pro-audio for a living.
I've owned four of the JBL's and they are great subs, I purchased them after researching everything from about $700 to $1500 range and talking to the folks at Pro-Sound Web.