Finally! its been like 2 years since have that problem. I got a ROG SWIFT PG278Q at 144hz with a g-sync and other 2 monitors at 120hz 1080p, my clock speed is 1189mhz idle, not normal and also power usage. I used to have all 3 120hz monitor, no problem and very low idle. 144hz + seem have problem running high idle clock because 144hz? it shouldn't be. Not just ASUS ROG Swift PG279Q, other monitor at very high refresh rates have same problem.
Can't wait to get FIXED!