The most important question needed to be answered first is, "What will be the primary use or uses of the computer?" If gaming is the primary intent then then I would go with the 7600k as it will perform identical to the 6700k while being newer and about $100 cheaper. Games tend not to be able to uset the extra threads of the 6700k . If you will be doing a lot of audio video rendering or other computing tasks that can efficiently utilize more than 4 cores then go with the 6700k.
Do you realize you posted this thread in the AMD section?