Yeah Ghz, that was a typo :-)
I simply set the multiplier for cores and sync them all. Works stable at 4.3Ghz. Would go more but I need a better cooler. Tried to run it at 4.6Ghz and I was not happy about the temperatures since I have a 120mm liquid cooler. But by default the i5 6600k has a boost clock at 3.9Ghz. So, it boosts to 3.9Ghz when needed. Here is a link from Intel website
http://ark.intel.com/products/88191/...up-to-3_90-GHz
Btw, just updated BIOS to 1901 (was released a week ago and did not notice it) and took me like what 1 minute to set all the OC config :-))) So really it's not hard.