we have two s70610 and have had issues with print lengths as well when printing wallpapers... where the stripes must match as closely as possible. we use custom media adjustment in the printer (feed adjustment), not in the rip (caldera here). we have never really resolved it to our full satisfaction. i am still wondering what could be done to help it. what factors can influence the feeding precision? when printing larger jobs, can the rollers collect dust and lose traction little bit? can their traction change with their temperature (which probably increases the longer you print)? also the temperature or humidity in the room might have an impact (if it is different from the conditions at which the media adjustment was performed)? what about the tension check, can it negatively influence the feeding consistency? should it rather be turned off? (it is quite impractical beacuse the media will unwind so much and fall down on the floor...)
i would assume that the slower the print speed, the more accurate the feeding, so maybe slowing down might help you achieve better results (never really tried and measured it myself though).