If you're willing to spend extra then you can now avoid the silicon lottery on X299 CPUs thanks to OverclockersUK. They announced earlier today that there is now a range of i7-7740X, i7-7800X, and i9-7900X available in their store that have been delidded and pre-binned to run at certain speeds.
https://www.notebookcheck.net/Pre-binned-and-delidded-X299-CPUs-up-to-5-3-GHz-now-available-from-OverclockersUK.240364.0.html