lun471k :
Correct me if I'm wrong, but one would be better off getting a 2700x for roughly the same price as a 1900X, newer and about 5% faster overall.
Well it depends on what the rig is being used for, but yes, that is a correct assumption. The only reason you would consider a 1900X at this point is to provide the upgrade path for the 2990X.
pokeman :
I'd wager the 1900X wouldn't be worth it coming from a 4700k (4.2 mild OC).
I'd say you would wager correctly. Ryzen 2nd generation is a far better investment.