  Forthcoming projects such as DES, LSST, WFIRST, and Euclid aim to measure
weak lensing shear correlations with unprecedented precision, constraining the
dark energy equation of state at the percent level. Reliance on
photometrically-determined redshifts constitutes a major source of uncertainty
for these surveys. Additionally, interpreting the weak lensing signal requires
a detailed understanding of the nonlinear physics of gravitational collapse. We
present a new analysis of the stringent calibration requirements for weak
lensing analyses of future imaging surveys that addresses both photo-z
uncertainty and errors in the calibration of the matter power spectrum. We find
that when photo-z uncertainty is taken into account the requirements on the
level of precision in the prediction for the matter power spectrum are more
stringent than previously thought. Including degree-scale galaxy clustering
statistics in a joint analysis with weak lensing not only strengthens the
survey's constraining power by ~20%, but can also have a profound impact on the
calibration demands, decreasing the degradation in dark energy constraints with
matter power spectrum uncertainty by a factor of 2-5. Similarly, using galaxy
clustering information significantly relaxes the demands on photo-z
calibration. We compare these calibration requirements to the contemporary
state-of-the-art in photometric redshift estimation and predictions of the
power spectrum and suggest strategies to utilize forthcoming data optimally.
