[bgnn]

One can always use clock repraters or a reclocking with a new PLL in the middle if the cable length gets too long and caused ISI (inter-symbol-interference). I don't think 30 ft requires this. At 60ft you might need it though it depends on the clock frequency. If the syncronization is done with low frequency clock (10 - 25 MHz or so) you don't need any of that. 60ft cable won't have too strong of an attenuation at those frequencies. GHz rate clock would be a problem.