What is your CPU usage with Xeon @ 1080p60 medium preset 6k bitrate?
Don't know, don't care. Looking at CPU usage is wasted time, the important thing are the duplicated/missed/lagged/whatevered frames. Those need to be close to zero. If its
very close to zero, then its likely you can move up to a better preset. If its in the 0.1% to 0.5% range, and you're unable to tweak other settings further, then you've probably found the sweet spot.
Focusing on CPU usage leads people down the wrong path. Some people think if the CPU isn't at 100% that they are wasting performance. They'll load up the CPU to 100% then whine when a particularly difficult frame shows up to be encoded, and their CPU has nothing left in the tank be able to handle it, and the frame is skipped, and over time this effect causes the output video to be jerky. Other people are under the impression that if the CPU usage is near 100% (or over some arbitrary threshold), that their computer is ready to freeze up, and they want it to be lower. There's no right answer to please everyone. This is because there's no right answer.
The truth is that CPU usage doesn't correlate well with good output video, but the dropped/skipped/lagged/duplicated/whatevered frames statistics do. So the latter is the only thing, other than viewing the recording or VOD with my own eyes, that I pay attention to.