Help Cool my rig

i7-9800x @ 4.5Ghz hitting 66*C under ~90% load. Problem exacerbated by the fact after ~30mins of maintaining ~90% load temperature slowly creeps up. I stopped it when CPU package temps were at 73*C (water temp was 31*C)

idle temp: ~20-25*C (ambient is ~21*C)

CPU Cooler is an Aquacomputer kryos cuplex NEXT VARIO w/ Vision on a 420GTX w/ 6xML140 RGB Pros in push/pull (front mounted intake) and 420GTS radiator w/ 3x ML140 RGB Pros in push (top mounted exhaust).

I suspect the culprit to be the 1200rpm max of the ML140s not being enough airflow to handle the size of the 1000D and dissipate the heat as the water temperature is very slow to dissipate. For example, from ~31*C, 25-30mins at idle, water temp is only down to 25.5*C. I basically leave the ML140s @ max as they really are quiet.

Anyone have any ideas what I can do to get the thermals on this rig more efficient? Hindsight, I suppose I should have gone w/ ML120s. But what am I supposed to do with these 9 ML140s and 420mm rads?

(Waiting for my 2080 TI Ultra FTW3 Hydrocoppers to come in, currently on an old GTX980 air cooled for testing)

After 10mins under 85% load.

Coolant temperature will never be the same as ambient except at startup.

Even at idle, heat is generated from the CPU. That's absorbed by the coolant. It'll only cool down so much.

Finally, where in the loop is the sensor? I'm not sure that you'll be able to get it much lower, regardless of how much air you push through the radiator.