A 10x difference in productivity between apprentice and master carpenters is the absolute outer limit of what’s plausible for an individual worker. Any higher than that and we’re mostly discussing coordination and management. 10x is a lower bound on the plausible productivity differential between programmers. In terms of the technical complexity of tasks they’re capable of the continuum from someone who worked through Learn Ruby the Hard Way and David Hartl’s book, a Lambda School grad, an MIT CS grad and Peter Norvig will be over 100 if not higher. In terms of economic productivity Ruby guy on upwork, patio11 billing at $30,000 a week and Jan Koum or Notch encompasses well over 1000x differences in productivity. Billing rates within a consultancy will often be over 10x between a junior consultant and a principal, for the same company, in the same line of work.