I'm gonna use whatever oil Kawasaki tells me to.
The temperatures you are seeing are quite high but not surprising. There are a couple of things you can do to protect the turbo from coking. You are already doing the first thing we would recommend which is to use a fully synthetic oil such as Mobil 1™. It will protect better against deposits and resist thermal breakdown than a conventional mineral oil.
If the Rotella works for you, that is great. I also race the Honda CX650 turbo and a common problem with those engines is the camshaft, follower, and valve tips have wear problems. Many of the CX owners swear by Rotella and don't seem to understand the cause of their problems. The CX was one of Honda's few bike motors with pushrods and these all seemed to have wear problems that a better oil could have prevented. A good strategy is if you plan to vary from the manufacturer's oil recommendation, you might want to buy an extended warranty and hope they don't ask what oil you used.