Hi, Cycles can use CPU or GPU and my GTX 760 is about 3-4 times faster than my i5 3570k.
If you have a strong CPU you need a high end Nvidia GPU GTX 770/80 3-6 GB.
Also when will blender cycles be albe to render smoke n fire with GPU?
Nobody knows, Volume is working but not enabled and smok/fire not work at all.