Hotter temperatures and slower clock rates are expected, but how much of a performance dip can we really expect? Early benchmark tests show the i9-9900K trailing by about 10 percent or more when on a laptop compared to a full-size desktop PC.
https://www.notebookcheck.net/The-Core-i9-9900K-is-about-10-to-15-percent-slower-on-laptops.355161.0.html