Since the 6700K is about 10% faster for a given clock speed, you are looking at about a 3.3GHz to 4.4GHz comparison in equivalent clocks. The 5820 has six cores so the effective speed is about 6X3.3GHz vs 4X4.4GHz for the 6700K. This gives you a factor of 19.8 for the 5820 and 17.6 for the 6700K. This is pretty close. I would go with the newer and lower power 6700K. You could overclock it to 4.5GHz and equal the speed of the 5820K.