Z270 K6 BIOS Setting for Watercooler

Right off the bat though I am seeing a whole lot of extractor fans and not a whole lot of intake. This isn't ideal, while yes you will be pumping out the warm air from the case faster you are also sucking air in through every gap, hole and grill in your case due to the negative pressure inside. Negative pressure is popular with some builders but it has to be within reason. Too much and you run into the situation where you are just spinning fans with not a lot of air getting through them. Even water cooling used air to cool the coolant, air cooling requires air, too much of a vacuum inside your case and you end up with less air going though your radiator. 

I am not going to get any more technical here, this is a highly subjective topic and in many cases the orientation of the radiator fans makes very little difference. In my experience though, this is how I like to set things up:

Radiator as exhaust (pulling air from inside the case and blowing it out of the case):

All front fans as intake, rear fan as exhaust and radiator mounted on the top of the case also as exhaust.

Radiator as intake (pulling air from ouside the case and dumping it inside):

Radiator mounted on the front of the case as intake with at least 1 other fan doing the same, top fans as exhaust, rear fan as exhaust.

Both these setups should perform more or less the same. With the rad intake config your GPU and VRMs may run a little hotter and with the Rad as exhaust your CPU may run a little hotter but in both situations we are talking minimal figures.

What you have now is not properly balanced, it sounds like someone went on to an enthusiast forum and read "negative pressure is best for cooling" and went the whole way with all fans as exhaust. That isn't what negative pressure being best means, it means leaning toward not all out. Fans should always be set up more or less balanced with one maybe 2 (with loads of fans) fans tilting the case pressure to positive or negative. I personally prefer positive pressure, it means less dust buildup in the case.