If you get a "convergence is questionable" warning, then I would not use that result. Although both GENMOD and LOGISTIC estimate parameters by maximizing a log-likelihood, they might not use the same optimization method or starting conditions, so one could converge and the other not. The LOGISTIC doc says "the maximum likelihood estimation is carried out with either the Fisher scoring algorithm or the Newton-Raphson algorithm" and the default technique is Fisher scoring, which is an iteratively reweighted least squares algorithm. For details, see http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_logistic_sect033.htm
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