Error corrected, matched pair CAN bus maxes out at 500 Khz; this design has nothing with matched termination and different cable lengths, so is obviously going to be much worse. If you're curious about how much worse, start here:
https://en.wikipedia.org/wiki/Reflections_of_signals_on_cond...
http://www.smar.com/en/technical-article/inductive-coupling-... https://en.wikipedia.org/wiki/Distributed_element_model
http://www.connectworld.net/cable-length.html