This is a quote from the Top Wishes Feedback
“DirectX12](DirectX 12): Ongoing effort of stabilization and optimization that will roll out this year.”
As far as overall CPU, the main focus I can see is in regards to memory leaks.
Eliminating these will give a big help to reducing the load on them.
The long flight CTD bug is one example of this and has been widely reported.
The other memory leak is this thread in regards to complex airports.
After playing a few hours, FPS drops from 40 to 5FPS - #1590 by HybridNZ