I believe it's just how the game is currently programmed. I have an i7 with SLI graphics and it will munch up 100% CPU for me too at times.
Here is the fix (workaround) though. Launch the game, go into your task manager and change the CPU affinity. I run Rising World off of just two cores without issue (one might suffice!) and the other cores run the OS and other applications just fine.
P.s. in case you need help with this - set process affinity

