S!
Luthier has stated they have improved the use of multiple cores in recent patches even the RTS option is not in conf.ini anymore. So you should be just fine. CrossFire can cause stutters and all, but seems that those with CrossFire use the LostPlanet2-profile in the settings and it helps. I still use a single card due all the problems SLI/CrossFire seems to induce in games. I also linked 12.7 beta drivers for AMD, they work nicely with CoD as well.
Have fun with your rig
It should be enough to run CoD easily.