That depends, the binning process means that products using the same die layout can have different characteristics. We don't yet know to what extent Ryzen is binned but here's a possibility: the 65W 1700 is made from cherry-picked dies that tolerate especially low voltages, the premium 1800X is made from dies that tolerate especially high clocks, and the 1700X is made from leftovers that didn't qualify for either.

https://en.wikipedia.org/wiki/Product_binning