TechPowerUp heard from AMD that the eight-core "Summit Ridge" dies that are used for the new Ryzen Threadripper processors are heavily binned.
The company selects only the top 5 percent performing dies for Threadripper to ensure these processors have the best possible power and performance characteristics:
AMD requires the highest grade "Summit Ridge" dies to use in Threadripper chips, to keep electrical leakage to the minimum, so the chips can run as cool as possible, with the least power-draw. Choosing the best dies could also ensure that Threadripper chips have the highest overclocking-headroom taking into account other electrical and thermal constraints. A 7-series chip such as the 1800X could still achieve higher clocks than a Threadripper chip, in that sense.