Yeah crossfire is known to scale better than sli at the uppper end.
About your build. I'm not a huge fan of the Cosmos myself, but thats due to looks. I can't comment on how good it is. there are a lot of good new cases that have just come out that you might want to check out also. The storm sniper, storm scout, panzer box, etc.
I would get a 3rd party cooler, as i didn't see you list one. You can get an lga1336 bracket for the core contact freezer, That should do you fine.
Other than that I think its solid.