In a printing system capable of printing and outputting collated sets of plural duplex copy sheets from input job sets of plural page images using a trayless duplexing buffer loop path of a known normal plural copy sheet length for recirculating the copy sheets imaged on one side back to be imaged on their opposite sides; operating in a continuous loop burst-interleave mode, using a variable speed duplex drive, for driving at least a major portion of the duplexing path sheet feeders at at least two different sheet feeding speeds so as to initially feed a limited number of the sheets to be printed on one side, less than the duplexing path length, at full rate without skips, to the duplexing path to be selectively partially fed therein at substantially higher than normal velocities, and to variably selectively reduce the velocity of the duplexing path with the initial sheets therein, to generate sheet interleaving spaces between these duplexing path sheets, so that they may be interleaved for their second side printing with subsequent first side prints until the final sheets of the job, which are also fed through the duplexing path at higher than normal speeds for different distances so as to close up interleaving spaces. This increases the duplex copying rate of the printing system by reducing or eliminating skipped pitches without requiring an increase in the given or normal printing rate.