An analysis has been performed to investigate the limits of high field commercial tokamak reactors. Variations of the maximum mechanical stress, the major radius and the performance parameter (where B0 is the magnetic field on axis and a is the minor radius) have been investigated to evaluate the potential impact of higher strength structural materials and higher field superconductors. For fixed values of major radius and stress, the tokamak parameters have been chosen such as to optimize machine performance. Increasing values of allowable stress correspond to decreasing capital cost and may be an effective approach to economic commercial fusion. The paper discusses prospects of using very high strength structural materials to provide a sufficiently high field for Ohmic dominated heating to ignition in power reactors with a major radius of about 6 m.